答:what if主句用一般将来时，从句用一般现在时，what if是一个省略句，它的完整结构是:what will you do……if……(如果……怎么样）这儿主从句时态对应原则就是我们常说的主将从现。
例如:what if it rains?(what will you do if it rains?)
what if you are faced with the rude boy?(what will you do if you are faced with the rude boy?)
