What is the function of a carbon sink？A．It regulates carbon emissions from human activitie

Why does the author use the term "duck factory" in paragraph 4?

A．To point out that ducks are the region's main product for export

B．To emphasize the area's value as a breeding ground for ducks

C．To illustrate the tremendous growth of the poultry industry

D．To show that the potholes are important to the region's economy

The word dot in paragraph 4 is closest in meaning to

A．cover

B．drain

C．warm

D．damage

in paragraph 4? Incorrect choices change the meaning in important ways or leave out essential information

A．The wetlands completely cover the landscape, making it difficult to grow crops and grass for grazing

B．The native grasses that grew in the potholes have been replaced with crops that are more beneficial

C．Except for the potholes region, the entire prairie has been converted to cropland and grazing land

D．Even though a large portion of the prairies is used for crops and grazing, the small ponds remain

The prairie potholes owe their origins mainly to

A．the variation in temperature throughout the year

B．the glaciers that melted at the end of the last Ice Age

C．the heavy rains that fall in the spring and summer

D．the increase in greenhouse gases in the atmosphere

The word alien in paragraph 2 is closest in meaning to

A．healthy

B．simple

C．cheaper

D．imported

What has taken place in the Great Plains grasslands during the last century?

A．The average annual rainfall has risen and fallen several times

B．Large parts of the prairie have been converted to agricultural use

C．Melting glaciers have formed numerous depressions in the soil

D．Scientists have transformed the region into one large carbon sink

All of the following statements are true of the northern Great Plains EXCEPT

A．Summer temperatures are very hot, while winter temperatures are very cold

B．An unbroken prairie now extends from the western mountains to the eastern forest

C．The original vegetation consisted of shortgrass, mixed grass, and tallgrass

D．A large number of small wetlands are found throughout the region

What does the professor think about computer sensors for buildings?

A．He thinks this is a superior. method for preserving buildings.

B．He finds the research on sensors for pistons very encouraging.

C．He is more concerned about the potential for people to be injured.

D．He doubts that the concept will result in design improvements.

Why does the professor say this:

A．He is introducing a new major point.

B．He is trying to get the students to participate.

C．He is drawing a conclusion about engineering.

D．He is disagreeing with his previous comment.

What happens to fill dirt during an earthquake?

A．It allows the building to sway.

B．It reduces earthquake damage.

C．It becomes unstable and collapses.

D．It creates mild shock waves.