【问】 我在Reading Laboratory，Book 2中读到这样一个句子：

Suppose you did your homework first.

从句所表示的是将来时间的事，它的谓语动词为什么要用过去时(did)呢?

【答】 在正式英语里，suppose引出的宾语从句的谓语动词要使用虚拟过去时(请与wish相比较)：

1. Just suppose everyone were to give up smoking and drinking. (CGEL)

让我们每一个人都戒掉烟酒。

2. Suppose her father turned her out of doors! (Wells)

想想她父亲真会把她赶出门!

3. Let’s suppose we each had ￡ 100 to spend——what would we buy with it?

我们大家来想想，要是我们每人都有一百英磅来花的话，我们会买些什么?

4. Suppose(that) one of us died. (CGEL)

假定我们当中有一个人死了。

但是，suppose的宾语从句的谓语动词也可以使用一般现在时：

1. Suppose he is lost，what would you do?

要是他迷路了，你怎么办?

2. But let us suppose that the Atlantic Ocean is now regularly crossed by enormous hover-craft. The hovercraft，with a thousand motor-cars on board，moves at 100 miles perhour，and is across the Atlantic in little more than one day.(复旦大学《英语》(三)，P.168)

让我们设想，现在有许多气垫船定期跨越大西洋航行。装运上千辆汽车的气垫船的航速每小时一百英里，气垫船只消花上一天的时间就能渡过大西洋。