问题补充:
His mother looked very tired,for she the house herself all day.
A. had cleaned
B. has been cleaning
C. had been cleaning
D. has cleaned
答案:
A. had cleaned
B. has been cleaning
(答案→)C. had been cleaning
D. has cleaned
解析:考查完成进行时。根据关键词all day可知应该使用完成进行时。再根据上文的looked可知应该使用过去完成进行时。