专家来讲：
1、补全句子：
I buy some pencils which are on the counter
把句子变成两个句子：
①I buy some pencils
②The pencils are on the counter
2、补全句子：
The lady who is standing behind the counter serves for me
把句子变成两个句子：
①The lady serves for me
②The lady is standing behind the counte