估计$\sqrt{35}$的值是 （   ）

小明要测量小灯泡的额定功率，实验桌上备有如下器材：符合要求的电源、额定电压为U₀的小灯泡、阻值为R的定值电阻、滑动变阻器、已调零的电压表、单刀单掷开关、单刀双掷开关各一个，导线若干。他设计了如图所示的电路进行实验。

  “Cool" is a word with many meanings．Its old meaning is used to express a temperature that is a little bit cold．As the world has changed，the word has had many different meanings．
  “Cool"can be used to express feelings of interest in almost everything When you see a famous car in the street，maybe you will say，“It's cool." You may think，“He's so cool," when you see your favorite footballer．
    We all maximize（扩大） the meaning of “cool". You can use it instead of many words such as “new" or "surprising"．Here's an interesting story we can use to show the way the word is used．A teacher asked her students to write about the waterfall（瀑布）they had visited．On one student's paper was just the one sentence, “It's so cool．Maybe he thought it was the best way to show what he saw and felt. But the story also shows a lack of words．Without “cool”，some people have no words to show the same meaning．So it is quite important to keep some credibility（可信性）．Can you think of many other words that make your life as colorful as the word "cool"？ I can．And I think they are also very cool．

1971年11月8日，美国《时代》周刊以周恩来总理为封面人物，并在封面上写着：“The Chinese are coming”。美国人发出这样感慨的主要原因是（    ）