The monument was constructed in honor of the explorer who was be

The monument was constructed in honor of the explorer who was believed ________ the river.
A、to have discovered
B、to have been discovered
C、to discover
D、having been discovered
【正确答案】：A
【题目解析】：用不定式的完成式表示动作发生在(定语)从句谓语动作之前。