it's getting late.I'd rather you __now.A.left B.leave 请解释原因,

would rather+从句,是一个常用的虚拟语气句型 Would rather+从句,谓语一般用过去时来表示现在或将来.其意为“宁愿……,还是…… 好些”“一个人宁愿另一个人做某事”.引导从句的that常省略.在谈到过去的动作时,谓语则用过去完成时.
例 John wants to see me today.I would rather he came to tomorrow than today.约翰今天想去看我.我宁愿他明天来看我而不是今天.(句中came不是表示过去而是表示将来)
We’d rather he paid us the money tomorrow.我们宁愿他明天付给我们那笔钱.
Don’t come tomorrow.I’d rather you came next weekend.明天别来.我希望你下周末来.
请注意 1） 如果谈到过去的动作,也就是表示过去已经发生的事情在选择上不恰当.此时,主句一般为I had rather ,其（that）从句则用过去完成时.例 Would rather you had not done that.我真希望你没有做那件事.
2）如果只涉及主语本人而不涉及另一个人,则would rather之后不接that从句而接have done结构.
例 I would rather have gone to the theatre than stayed home night.我真希望昨天晚上去看了戏而不是呆在家里.He would rather be poor than have got money by dishonest methods． 他宁可穷也不愿意用不诚实的手段获取金钱.
Henry would rather that his girlfriend worked in the same department as he does．亨利希望他的女朋友和他在一个部门工作.