补充250题168

168. 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（B）

(E) which is more than had reported sightings  請問這是什麼語法結構，為什麼逗號後接 more than had been sighted?

名称好像是“补足语”

不好意思還有一個疑問，為什麼more than 前面不用加those，還有補足語的結構是什麼？