4. A savings instrument has an "interest rate" associated with it; this refers to the rate which the money in the instrument increases during a certain period of time.
1、
【正确答案】
1、C。which→at which。关系代词which在此引导的是一个定语从句，并且在此应该用“介词+关系代词”这个形式，因为前面的rate往往用于短语at a rate，此处的介词可以提前。