题目内容：

I have studied English or three years since I had come here.（改错）

优质解答

I have studied English for three years since I （had come）（把这两个词改为came） here.
自从我来到这里,我已经学了三年英语了.
主句为现在完成时态,since引导的时间状语从句应该为一般过去时,had come应该改为came.