After years of study, scientists figured out that living things, including human bodies, are basically made of amino acids, nucleotide bases, lipids and water. How could such complicated molecules have been formed and have started to interact in the primitive soup? Scientists were stumped.
Then, in 1953, two scientists named Harold Urey and Stanley L. Miller did a very simple experiment to find out what had happened on the primitive Earth. They set up some tubes and bottles in a closed loop, and put in some of the same gases that were present in the atmosphere 4 billion years ago—water vapour, ammonia, carbon dioxide, methane, and hydrogen.
Then they shot an electric spark through the gases to simulate bolts of lightning on the ancient Earth, circulated the gases through some water, sent them back for more sparks, and so on. After several days, the water that the gases had been bubbling through turned brown. Some new chemicals were dissolved in it. When Miller and Urey analyzed the liquid, they found that it contained amino acids—the very kind of molecules found in all living things.
When did scientists come to realize how the atoms and molecules on the Earth mostlikely combined to make living things?
A.4 billion years ago.
B.After seven days.
C.Many years ago.
D.In 1953.
第1题
A.既不能移动,也不能改变大小
B.仅可以移动,不能改变大小
C.仅可以改变大小,不能移动
D.既能移动,也能改变大小
第2题
在Windows中,对话框是一种特殊的窗口,它()
A.既不能移动,也不能改变大小
B.仅可以改变大小,不能移动
C.既能移动,也能改变大小
D.仅可以移动,不能改变大小
第3题
A.仅可以移动,不能改变大小
B.既能移动,也能改变大小
C.既不能移动,也不能改变大小
D.仅可以改变大小,不能移动
第4题
把Windows xP的窗口和对话框作一比较,窗口可以移动和改变大小,而对话框()。
A.既不能移动,也不能改变大小
B.仅可以移动,不能改变大小
C.仅可以改变大小,不能移动
D.既能移动,也能改变大小
第5题
把Windows的窗口和对话框作一比较,窗口可以移动和改变大小,而对话框()
A.既不能移动,也不能改变大小
B.仅可以移动,不能改变大小
C.仅可以改变大小,不能移动
D.既能移动,也能改变大小
第6题
A.可以移动窗口,可以改变大小
B.可以移动窗口,不可以改变大小
C.不可以移动窗口,可以改变大小
D.不可以移动窗口,不可以改变大小
第7题
A.既不能移动.也不能改变大小
B.仅可以改变大小.不能移动
C.既能移动.也能改变大小
D.仅可以移动.不能改变大小
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