关于虚拟语气的一道题目.She does not stick to her exercises and a balanced diet.If ...

题目

关于虚拟语气的一道题目.She does not stick to her exercises and a balanced diet.If ...
She does not stick to her exercises and a balanced diet.If she （did）,she would rermain slim and healthy.括号部分为什么不能填（had done）呢?

答案

后面是would 所以前面用过去式