When I am down my parents will do what every parent will do is to hug me tighter and te

问题补充：

When I am down, my parents will do what every parent will do, is to hug me tighter and tell me I am the best.

A. which

B. what

C. that

D. who

答案：

(答案→)A. which

B. what

C. that

D. who

解析：通过分析句子结构，可知这个句子中包含一个非限制性定语从句，且关系词在从句中作主语，指代前面的整个主句内容，故用which。That和what 不能引导非限制性定语从句。Who先行词应该是人。