The bus at six, but it arrived an hour later.
A. should arrive
B. had arrived
C. should have arrived
D. must arrive
网友回答
A. should arrive
B. had arrived
(答案→)C. should have arrived
D. must arrive
解析：考查情态动词用法。Should have done被应该做某事，实际上却未做；根据下句的arrived说明本句是对过去情况的虚拟，故使用“情态动词+have done”的形式；句意：公交车本应该在6点到，但是却晚来了一个小时。故C正确。