I ____ here for four years,by next summer I shall have graduated

I ____ here for four years,by next summer I shall have graduated.
A、shall study
B、have studied
C、shall be studying
D、have been studying
E、 
【正确答案】：D
【题目解析】：我在这里学习四年了,到明年暑假,我就（已经）毕业了。表示从过去到现在，并且会持续到未来，因此要使用现在完成进行时，have been studying。