you should b-- a present for Allen on his birthday.

问题描述:

you should b-- a present for Allen on his birthday.
填bought还是buy?句中能看出是过去时态吗?
如果是将来时态就应该是you should buy a present for Allen for his birthday.
风唱梵音

buy也可以,have bought 也可以.
buy 的话意为 你应该为Allen买个生日礼物.(将来时)
have bought 的话意为 你本应该为Allen买个生日礼物的.(实际上没买)(过去虚拟时)