题目

You were very impolite to him, for ______ you should make an apology to him, I think, A. this                      B. which C. what                      D. that   答案：B此题属于“介词+关系代词”引导的定语从句。先行词指物时关系代词用which，指人时用whom。若方程nx2-3x+1=0是关于x的一元二次方程，则n________．