用be动词的三种形式am,is和are填空.

You are a good boy; （"You" 后一般现在时的Be动词固定用"are”）
Zhang Qing is seven;（"Zhang Qing" 为单数第三人称"is"）
His pen and my pen are black;（"His pen and my pen" 可见主语为复数选用"are"）
What color is your ruler?("Your ruler" 为单数第三人称选用"is")
Bob's telephone mumber is 345-8886.("teleohone number" 为单数第三人称故选用"is")
备注：Be 的现在时三种形式 am,is,are 其实还是比较容易分的,最主要的是找到主语,根据主语判断用哪一种形式.
am 的主语毫无疑问是 I；
are 的主语就分两种形式：
第一：主语是You;
第二：主语是复数；
is 的主语为第三人称单数.

1A 2I 3A 4I 5I 好好想想为什么

1，are
2，is
3, are
4, is
5, is

you are a good boy, zhangqing is sevenm his pen and my pen are balck, what color is your ruler, Bob's telephone number is 345-8886

1. are 2. is 3. are 4. is 5. is