(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
网友回答
A. Having explained
B. Having been explained
C. Though it was explained
(答案→)D. It was explained
解析：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。