一題英文請教 - 金融業討論

The key players in the energy market, ____________ heavy capital investment,
have little interest in innovation
in innovation.


1.which to require
2.requiring
3.which it requires
4.required

答案是2
請問是因為當形容詞修飾主詞嗎?
還是又省略了什麼關代?
常因類似考題有時選4有時又要選2而搞混~~

--