291. 首先，你必须努力工作。
[误] At first, you must work hard.
[正] First, you must work hard.
注：at first 指“起初，开始的时候”，如：At first I found this question very difficult, but finally I managed to
answer it（一开始我觉得这个问题很难回答，不过最后我还是答出来了）；first 才是指“首先”。又如：First, let me introduce myself（首先，请允许我介绍一下我自己）。