mother made a promise __i behaved well,she would buy me a bike

题目

mother made a promise __i behaved well,she would buy me a bike
that
that if
if
whether

答案

答案 that if.
我作过一道这样的题,
that 只表示引起了从句,
that if 是在叙述了后还存在选择 ,
那就是(that)如果（if）我表现的好,就给我买一台
if /whether 只表示如果,不奶奶感引起从句