There's no saying how he'll react.

很难说他会有何种反应。

We should send out written invitations to the party or there's no saying how many people will turn up.

我们应该发出晚会的书面邀请，否则说不准到底有多少人会来参加。

I didn't even know her, before this. There's no saying exactly what the background is, but I found it sad.

在此之前我从未了解过她。我说不准她的家庭背景到底是什么样的，但是我觉得这件事让人很难过。