. The reason for all the changes being made to us yet.A. has not explainedB. has not been

问题补充：

. The reason for all the changes being made to us yet.

A. has not explained

B. has not been explained

C. did not explained

D. were not explained

答案：

A. has not explained

(答案→)B. has not been explained

C. did not explained

D. were not explained

解析：考查时态。根据题中时间状语yet可知用现在完成时态，根据语境可知用被动形式。句意：正在作所有改变的原因还没有向我们解释。