By the end of last year, we seven hundred English words.
Alearned
B. have learned
C. had learned
Dwould have learned
网友回答
A. learned
B. have learned
(答案→)C. had learned
D. would have learned
解析：考察时态，by是完成时的标志，by后面跟什么时间，主句就用什么完成时，根据last year过去时间可知，主句应该用过去完成时