We have kept ___ our friendship by writing to each other,so we are true friends.

问题描述:

We have kept ___ our friendship by writing to each other,so we are true friends.
选项:
a、up
b、back
c、off
d、down
麻烦解释下该如何选择

我是英语专业的.四个选项的意思分别是.
A.保持,继续,维持,跟上(时代)
B.隐瞒,保留,阻止,阻挡
C.不接近,避开
D.抑制(控制)
所以选择A.我们通过写信维持我们的友谊.