问题补充：
It four years since we to learn English.
A. Is , begin
B. has been , began
C. has, been
D. had been ,began
答案：
A. Is , begin
(答案→)B. has been , began
C. has, been
D. had been ,began
解析：句意：自从我们开始学英语已经有四年了。since,自从……，后加过去的时间点或过去时态的句子，是现在完成时的标志词，表示一个动作从过去就开始了一直持续到现在。如果主句是一段时间，也可以用一般现在时代替现在完成时。A项，begin的时态不正确，故选B
