Believe it or not, the matter, we argued for a long time, was in fact related to our stu

网友回答

A. over it
B. with them
(答案→)C. about which
D. for which
解析：考察定语从句的介词。本题定语从句的先行词是the matter。后面的定语从句中有固定搭配argue with sb about sth因为某事与某人争吵。本题定语从句中使用which指代先行词作为介词about的宾语。句意：信不信由你，我们争吵了很长时间的那个事情实际上是与我们的学习有关的。故C正确。