One thing ____we should keep in mind is that every big thing comes from the small details.
问题描述：
One thing ____we should keep in mind is that every big thing comes from the small details.
A.who B.what C.that D.whose 这里为什么只能用that而不能用what 呢,
答
that是关系代词,代替one thing.如果前面没有one thing 就可以用what代替we should keep...