Opportunity knocks (at the door) but once.

良机难再。

If opportunity knocks , I will take it.

如果机会来临，我会抓住。

Luck is when opportunity knocks and you answer.

运气就是你对降临的良机的回应.

Opportunity knocks but once, so we must make the most of it.

机不可失 ，失不再来，所以一定要把握时机。

A：Well, I am hoping to get an offer of a better position. If opportunity knocks, I will take it.

我希望能获得一份更好的工作，如果机会来临，我会抓住。

A: Well, I am hoping to get an offer of a better position. If opportunity knocks, I will take it.

A: 我希望能获得一份更好的工作，如果机会来临，我会抓住。

Well, I am hoping to get an offer of a preferable position. If opportunity knocks, I will get it.

我期望能得到一份较好的任务。假如机遇来临，我就会抓住它。

A： Well, I am hoping to get an offer of a better position. If opportunity knocks, I will take it.

我希望能获得一份更好的工作，如果机会来临，我会抓住。