What if ...结构可以看作无动词主句。所谓无动词主句，实际上是一种缩略结构，它没有任何形式的谓语动词。当然，我们可以把它扩充为一个完整的主句。需要注意的是，我们所说的无动词主句没有谓语动词，不是讲的从句中没有谓语动词。请看下面的例子。
What if they do not come? 如果他们不来，该怎么办？（What if they do not come?=What will happen if they do not come?）
What if they don't agree with us? 他们不同意我们的意见怎么办呢？（What if they don't agree with us?=What will happen if they don't agree with us?=What does it matter if they don't agree with us?）
What if I get sick? 如果我生病了怎么办？（What if I get sick?=What shall I do if I get sick?）
What if nobody shows up? 如果没人到场将会怎样？（What if nobody shows up?=What happens if no one shows up?）
