The degree you maintain your mental health may depend on certain

The degree you maintain your mental health may depend on certain simple environmental factors.
A、which
B、to which
C、that
D、to that
【正确答案】：C
【题目解析】：本题考察定语从句，you maintain your mental health已经是个完整的句子，不缺少成分，所以用that作为关系词。