问题补充:
—You should have thanked her before she left.
—I meant , but when I was leaving I couldn’t find her anywhere.
A. to do
B. to
C. doing
D. to have done
答案:
A. to do
(答案→)B. to
C. doing
D. to have done
解析:这是一组对话。上文,你应在走之前感谢她。下文,我打算这样做,但是当我要离开时去找不到她。这是动词不定式的省略形式,后面的do sth一起省略,这里必须要用mean to do而不是doing(前者是“打算做某事”,后者“意思是,意味着”,意思不对)。A的do是一个实义动词,需要加宾语sth,动词不定式的省略是到to为止的(有时表示过去要加上have),后面的do sth要一起省。