問題詳情

134. An estimated five and a half billion tones of carbon ______ released into the atmosphere each year by burning of coal, oil, and synthetic fuels.
(A) have been
(B) have
(C) has
(D) has been

參考答案

答案：A
難度：適中0.545455
統計：A(12),B(3),C(0),D(3),E(0)