写出C4H8所有链烃的同分异构体并命名。

阅读理解。

     When Webster was young, he was a teacher. But he quickly became tired of the books he used in

classes. They were all about the English people and places. Since he wanted books that would be

interesting to American children, he wrote three books with many American examples.

      Webster worked industriously (勤奋地) to change the spelling of American English. He wanted

words to be spelled in the same way they were pronounced (发音). For example, he thought the word

"laugh" should be spelled "1af".

     One day he walked into a print shop and gave the boy there a piece of paper. "Young man," he said,

"when you print any please don't spell as English people do. For example when you print these words

"theatre, centre, colour, and labour (劳动)", please always print them as "theater, center, color,

and labor'." The boy studied it and answered, "OK, but I must ask my boss first."

      With the money he made from his books, Webster could start his work, which took him more

than twenty years to finish. In 1828, the first American English dictionary was born. And today,

Webster's dictionary is thought to be the most important American dictionary in the whole world.

1. What kind of books did he use when Webster was young? [ ]

A. Books about Great Britain.

B. Books about the USA.

C. Books about both Great Britain and the USA.

D. Books that were very interesting.

2. Webster decided to change the spelling of American English because _____. [ ]

A. he was born in America

B. there were too many mistakes in them

C. American children were not interested in them

D. they were not spelled in the same way they were pronounced

3. On the paper Webster gave the boy were the words _____. [ ]

A. easy to say

B. that didn't sound well

C. whose pronunciations he wanted to change

D. whose spellings he wanted to change

4. Webster began to write the first American English dictionary before the year _____. [ ]

A. 1808

B. 1820

C. 1828

D. 1858

某块正方形操场，边长为50米，沿操场四周每隔1米栽一棵树，问栽满四周一共可栽多少棵树( )

A．199
B．200
C．201
D．202

若函数f（x）=lg（ax²+2x+1）的值域是R，则a的取值范围是______．

RC电路时间常数τ与下列关系正确的是（）

A、τ＝RC

B、τ＝R/C

C、τ＝C、/R

D、τ＝1/（RC）

生物多样性包括基因多样性、（）和（）三个层次的内容。