刘振民E9-13

Since the movie was released seventeen UFOs have been sighted in the state, which is more than had been sighted in the past ten years together.

A  which is more than had been sighted

B  more than had been sighted

C  more than they had sighted

D  more than had reported sightings

E  which is more than had reported sightings

答案是B，但我不理解Since the movie was released seventeen UFOs have been sighted in the state这句话中，was released和have been sighted到底谁是真正的谓语，如果是，那另一个作什么成分呢?