問題詳情

28. Although the causes of cancer ____, we do not yet have any practical way to prevent it.
(A)are being uncovered
(B)have been uncovering
(C)are uncovering
(D)have uncovered

參考答案

答案：A
難度：適中0.5
統計：A(0),B(0),C(0),D(0),E(0)