If you ____careful,you will fall off the bike.

题目

If you ____careful,you will fall off the bike.
A.don't be B.aren't C.are D.won't be
望好心人能顺便说明解题原因,万分感谢

答案

aren't
主句 will fall 是将来时.
if 引导的从句,主将从现,所以 从句用现在是.
aren't翻译如下：
如果你不小心,就要翻车.