用法说明 lest, in case, in case of

lest较正式，其义为“恐怕”、“惟恐”或“担心”。作“担心”解时，常与fear, be afraid of, be anxious等连用，例如：

He ran away lest he (should)be caught.他怕被抓，因而逃走了。

I was afraid lest she might be offended.我担心把她给得罪了。

in case意思为“以免”。in case of表示“假如某事发生”。试比较：

I don't let him climb trees in case he tears his trousers.我不让他爬树，以免撕破裤子。

In case of fire, ring the alarm bell.如果失火，就按警铃。