問題詳情
21. An investigation ________ into several engine break down incidents possibly linked tocontaminated fuel.
(A) have being carried out
(B) has being carried out
(C) was being carried out
(D) is being carried out
參考答案
答案：D
難度：非常困難0
統計：A(0),B(1),C(0),D(0),E(0)