（3分）开链烷烃的分子通式为C_nH_2n+2（n为正整数），分子中每减少2个碳氢键必然同时增加1个碳碳键，可能形成双键或三键也可能是环状烃，但都称之为增加一个不饱和度。例如：CH₃C≡CCH₂CH=CH₂其不饱和度为3。如图4-2篮烷的结构，其分子式为         ，不饱和度为__ ____，其一氯取代物有      种。

用括号内所给动词的适当形式填空。

1. Look! The children _________ (play) football on the playground.

    They _________ (play) football every Sunday afternoon.

2. Please be quiet! We _________ (listen) to the song You and Me.

3. — Mrs. Green likes children very much, doesn't she? 

    — Yes, that's true. She __________ (write) a children's book these days.

4. How many lessons __________ Peter __________ (have) on Monday?

5. It's fine today. The sun __________ (shine).