题目内容

Now, listen to the passage.
What do plants do when they are thirsty？
[A] They give out faint cries.
[B] They make noises to drive away insects.
[C] They extend their water pipes.
[D] They become elastic like rubber bands.

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一段长度100bp的DNA，具有4¹⁰⁰。种可能的序列组合形式。

A] measurement
[B] calculation
[C] guarantee
[D] optimism

All of the following facts about the telegraph and the Internet are true EXCEPT that
[A] both develop from the most advanced science of their time.
[B] they are operated similarly in technical terms.
[C] both help to change the way we do business and communicate.
[D] both facilitate the communication between cultures and ethnic groups.

在核酸双螺旋(如DNA)中形成发夹环结构的频率比单链分子低。发夹结构的产生需要回文序列使双链形成对称的发夹，呈十字结构。