问题补充：
The twins has studied in this school .
A. two years ago
B. since two years ago
C. for two years ago
D. since two years
答案：
A. two years ago
(答案→)B. since two years ago
C. for two years ago
D. since two years
解析：与现在完成时，连用的时间状语为since +一段时间+ago,for +一段时间，故选B
