What if ...結構可以看作無動詞主句。所謂無動詞主句，實際上是一種縮略結構，它沒有任何形式的謂語動詞。當然，我們可以把它擴充為一個完整的主句。需要註意的是，我們所說的無動詞主句沒有謂語動詞，不是講的從句中沒有謂語動詞。請看下面的例子。
What if they do not come? 如果他們不來，該怎麽辦？（What if they do not come?=What will happen if they do not come?）
What if they don't agree with us? 他們不同意我們的意見怎麽辦呢？（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? 如果我生病了怎麽辦？（What if I get sick?=What shall I do if I get sick?）
What if nobody shows up? 如果沒人到場將會怎樣？（What if nobody shows up?=What happens if no one shows up?）
