问题补充:
More than a dozen students in that school abroad to study medicine last year.
A. sent
B. were sent
C. had sent
D. had been sent
答案:
A. sent
(答案→)B. were sent
C. had sent
D. had been sent
解析:be sent abroad 表示“被派往国外”。有明确的过去时间状语last year,所以用一般过去时的被动形式。