Question

These students will graduate from the university next summer, ____ they will have studied here f

These students will graduate from the university next summer, ____ they will have studied here for four years
A.by then
B.by that time
C.by what time
D.by which time
每个选项都解释一下，谢谢！

Answer 1

这群学生在下个夏天就可以大学毕业了，____他们将会在这学习了4年。
A.by then。。。指的是下个夏天之后的时间
B.by that time。。。指的是下个夏天的时间
C.by what time。。。指的是将要完成学习的4年时间
D.by which time。。。指的是将要完成学习的时间