1、用Let's…?表示“让我们”(包括双方在内)做某事“这一建议时要用以Let's 开头的祈使句。而Let us在表示让我们做某事时,不包括对方在内。如:Let's go and see the pandas. Let us go,will you?让我们去吧,好吗?
2、用Why not…?Why not…?意思是:为什么不……?后接不带to的不定式(即动词原形)。Why not…?是省略了主语的省略形式,完整句Why don't you/they/we…?如:Why don't you go with me? Why don't you try again?=Why not try again?
3、用What about…?意为“……怎么”后可接名词、的代词和动名词。如:What about going out for a walk?I'm going to the park.What about you?