阅读理解

A

　Here are some English study skills for beginners.

　　★Listening

　　Listening is a great way to improve your pronunciation and intonation (语调). You can start by listening to short stories for children because they are usually easy.

      ★Reading

　　Reading is a good way to help you learn new words. And it will also help you learn English grammar. Children's books are great for beginners.

       ★Vocabulary

　　When you come across new words in the reading, write them down in your notebook. You can write down the translation in your native language to help you understand.

  　★Speaking

　　While doing your reading exercises, read them aloud.You can also look for some articles on the Internet to read.

 　　Learning any language needs practice—lots of practice.You don't have to spend hours studying each day; just 30 minutes a day for four or five days a week will help you improve it.

如图是由五个相同的小立方块搭成的几何体，则它的俯视图是（　　）

解：设S=1+2+3+…+100，  ①

  则S=100+99+98+…+1，②

  ①+②，得

  2S=101+101+101+…+101．

  (两式左右两端分别相加，左端等于2s，右端等于100个101的和)

  所以2S=100x101，

  S= $\frac{1}{2}$ ×100X101=5050  ③

    所以1+2+3+…+100=5050．

后来人们将小高斯的这种解答方法概括为“倒序相加法”．

请解答下面的问题：