-We'll finish our middle school study in a few months.

问题描述:

-We'll finish our middle school study in a few months.
-Yes,time files!Three years________________________.
A.is passing by B.has passed by
C.have passed by D.are passing by
-Kang Kang,how do you learn English so well?
-____watching English movies and try to repeat the actors.
A.In B.For
C.By D.On
以上2道我知道答案但不知道为什么,请用简洁易懂的语言详细解释一下.
看了现有回答,我还是很迷糊,能否详细讲讲每个选项呢?

第一题是完成时,站在现在看过去的中学生活,表示3年过去了
第二题是因为 by doing sth是表示依靠做什么而...,是固定用法