He is ( ) careful that he always looks over his exercises to make sure the right answer.

选A，不能选D
因为so that和such that都有如此。。。以至于的意思，但so后面加形容词，而such后面加一个名词词组。
题目是careful，形容词，所以用so

so ..that..这是固定搭配。。
"如此。....以至于...."

so ..that..这是固定搭配。。不能选D

A.so