if you ____ free tomorrow you can go shopping with us.A are B will be C will D are going to be

问题描述:

if you ____ free tomorrow you can go shopping with us.A are B will be C will D are going to be
为什么句中用are?而不用will be ,will,are going to be?

亲,if 从句中一般将来时用一般现在时代替