在项目投资决策中，净现金流量是指经营期内每年现金流入量与同年现金流出量之间的差额所形成的

听力原文： One way that scientists learn about man is by animals, such as mice, rats and monkeys. The scientists in this laboratory are experimenting on mice. They are studying the relationship between diet and health. At this time over one hundred experiments are going on in this laboratory.

In this experiment, the scientists are studying the relationship between the amount of food the mice eat and their health. The mice are in three groups. All three groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating one cup of food each day, the second is eating two cups, and the third group of mice is eating three cups.

After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Al so they are living longer. Mice usually live for two years. Most of the mice in this group are still alive after three years. The second group of mice is normal weight. They are healthy, too. They axe active, but not as active as the thinner mice. But they are only living about two. years. The last group of mice spends most of the day eating or sleeping. They are not very active. These mice are living longer than the scientists thought: about a year and a half. But they are not healthy. The experiment is still going on. The scientists hope to finish their studies in two years. 32．According to the passage，what animals are often used by scientists to learn about man？

(33)

A．Mice.

B．Rats.

C．Monkeys.

D．A, B andC

根据下面内容，回答题：

A group of scientists rowing toward the center of a lake saw something shocking. They turned back as fast as they could. What had they seen？ The lake was boiling!

The group was investigating a crater lake in the mountains of St. Vincent. A crater lake is the mouth of a volcano that has been dormant for some time and has filled with water.

This particular crater was the tip of a volcano called Soufriere， which erupted last in 1902. Since that time， it had not shown any signs of action. But in the fall of 1971， mountain climbers who had hiked near the lake returned to the lowlands with strange stories. They said the water had turned yellow and was giving off a smell like burnt eggs. A seething fog was rising from the lake"s surface.

Local scientists rushed to Soufriere to see if this might be the beginning of a new volcanic explosion. They found a huge black mass in the middle of the water. It was a great blob 1，000 feet long and 300 feet wide. Lava had pushed up through the bottom of the lake and formed a new island.

The investigators wanted to make sure that the volcano was safe， and that the lava would not overflow into the surrounding countryside， But they could never reach the island to study it， because the lava was so hot that the water around it bubbled and boiled.

This passage is about________. 查看材料

A.mountain climbing

B.a boiling lake

C.a new volcanic island

D.a mysterious blob

听力原文： One way that scientists learn about man is by animals, such as mice, rats and monkeys. The scientists in this laboratory are experimenting on mice. They are studying the relationship between diet and health. At this time over one hundred experiments are going on in this laboratory.

In this experiment, the scientists are studying the relationship between the amount of food the mice eat and their health. The mice are in three groups. All three groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating one cup of food each day, the second is eating two cups, and the third group of mice is eating three cups.

After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Also they are living longer. Mice usually live for two years. Most of the mice in this group are still alive after three years. The second group of mice is normal weight. They are healthy, too. They are active, but not as active as the thinner mice. But they are only living about two years. The last group of mice spends most of the day eating or sleeping. They are not very ac tire. These mice are living longer than the scientists thought: about a year and a hell But they are not healthy. The experiment is still going on. The scientists hope to finish their studies in two years.

(33)

A．Mice.

B．Rats.

C．Monkeys.

D．A, B and C

听力原文： One way that scientists learn about man is by animals, such as mice, rats and monkeys. The scientists in this laboratory are experimenting on mice. They are studying the relationship between diet and health. At this time over one hundred experiments are going on in this laboratory.

In this experiment, the scientists are studying the relationship between the amount of food the mice eat and their health. The mice are in three groups. All three groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating one cup of food each day, the second is eating two cups, and the third group of mice is eating three cups.

After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Also they are living longer. Mice usually live tot two years. Most of the mice in this group are still alive after three years. The second group of mice is normal weight. They are healthy, too. They are active, but not as active as the thinner mice. But they are only living about two years. The last group of mice spends most of the day eating or sleeping. They are not very active. These mice are living longer than the scientists thought: about a year and a half. But they are not healthy. The experiment is still going on. The scientists hope to finish their studies in two years.

(33)

A．Mice

B．Rats

C．Monkeys

D．A，B and C

听力原文： One way that scientists learn about man is by animals, such as mice, rats and monkeys. The scientists in this laboratory are experimenting on mice. They are studying the relationship between diet and health. At this time over one hundred experiments are going on in this laboratory.

In this experiment, the scientists are studying the relationship between the amount of food the mice eat and their health. The mice are in three groups. All three groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating one cup of food each day, the second is eating two cups, and the third group of mice is eating three cups.

After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Also they are living longer. Mice usually live for two years. Most of the mice in this group are still alive after three years. The second group of mice is normal weight. They are healthy, too. They are active, but not as active as the thinner mice. But they are only living about two years. The last group of mice spends most of the day eating or sleeping. They are not very active. These mice are living longer than the scientists thought: about a year and a half. But they are not healthy. The experiment is still going on. The scientists hope to finish their studies in two years.

(33)

A．Mice.

B．Rats.

C．Monkeys.

D．A, B and C.

What does the passage mainly talk about？

A．The three benefits provided by trees.

B．Trees and soil conservation.

C．The various uses of trees.

D．The different attitudes of the government and the villagers toward trees.

What does the passage mainly talk about？

A．The three benefits provided by trees.

B．Trees and soil conservation.

C．The various uses of trees.

D．The different attitudes of the government and the villagers toward trees.

What does the passage mainly talk about？

A．The three benefits provided by trees.

B．Trees and soil conservation.

C．The various uses of trees.

D．The different attitudes of the government and the villagers toward trees.

A．work to explain real, rather than theoretical or simplified situations

B．know that well-defined problems are often the most difficult to solve

C．are unable to express their data in terms of multiple variables

D．are unwilling to relax the axioms they have developed

A．work to explain real, rather than theoretical or simplified situations

B．know that well-defined problems are often the most difficult to solve

C．are unable to express their data in terms of multiple variables

D．are unwilling to relax the axioms they have developed