1.Sometimes it is necessary to be careful_____the right date to sit for a test.
问题描述：
1.Sometimes it is necessary to be careful_____the right date to sit for a test.
A.when choosing B.when you will choose C.when you have chosen D.when you chose
选哪一个and WHY?
答
A
这句话完整说起来其实就是when you are choosing...
这个时候如果主语和主句是一致的,可以省略you are