问题
选择题
(2013·宁夏银川一中高三第四次考试)________ scores of times, but he still couldn't understand it.
A．Having explained
B．Having been explained
C．Though it was explained
D．It was explained
答案
答案：D
D 考查句子结构。本句中的but是并列连词，由此可知but前后都是完整的分句。表转折意义的句中，but与though不能同时用，故D项正确。