Supposing (that) you are wrong, what will you do then?

假设你错了，那你会怎么办？

So, supposing that you are sitting in a company meeting and the presenter puts up the first slide.

那么假设你在公司开会，演讲者打开了第一张幻灯片。

But supposing he sees us?

可他要是看见我们呢？

Well, then, supposing we go and call on HIM?

那么，我们去拜访他怎么样？

There was his rapid glance at the house, and supposing himself unseen.

他飞快地瞥了一眼房子，以为没人看见他。