What some people don't realize is difficult life can be after they get addicted to drugs

问题补充：

What some people don realize is difficult life can be after they get addicted to drugs.

A. that

B. how

C. why

D. what

答案：

A. that

(答案→)B. how

C. why

D. what

解析：B 考察名词性从句。句意：有些人没有认识到一旦染上毒瘾生活会多么艰难。How多么，引导表语从句。