if you do not konw what it means,________________(查字典)我们老师给的答案是 refer to the dictionary额、我想问、为什么要用refer 不用referring【- -原谅我的无知】那什么时候用ing形式- -

问题描述:

if you do not konw what it means,________________(查字典)
我们老师给的答案是 refer to the dictionary
额、我想问、为什么要用refer 不用referring【- -原谅我的无知】
那什么时候用ing形式- -

一种if从句 ,if 引导状语从句,主句用祈使句
例: If you want to do it, do it as well as possible.