【题目】The twins, who their homework, were allowed to play badminton on the playground.
A.will finish
B.finish
C.have finished
D.had finished

【答案】D
【解析】句意：已经完成作业的双胞胎被允许到操场上打羽毛球。他们“被允许”用的是一般过去式，而完成作业是在被允许打羽毛球之前，属于过去的过去的动作，用过去完成时，所以选D。