1、necessary

必要的;必需的

I kept the engine running because it might be necessary to leave fast.

我沒讓發動機熄火，因為也許需要迅速離開。

We will do whatever is necessary to stop them.

我們要采取一切必要措施去阻止他們。

(結果或聯系)必然的，勢必的

Wastage was no doubt a necessary consequence of war.

巨大的損耗無疑是戰爭的必然結果。

Scientific work is differentiated from art by its necessary connection with the idea of progress.

科學工作與藝術的區別在于它與人類進步有著必然聯系。

如果必要的話

If necessary, the airship can stay up there for days to keep out of danger.

必要時，飛艇能在那里停留數天以躲避危險。

The army needs men who are willing to fight, when necessary.

軍隊需要在必要時愿意投入戰斗的軍人。

2、come back

回憶起;回想起

He was also an MP — I'll think of his name in a moment when it comes back to me.

他當時也是一位國會議員，他的名字我得想一下才能記起來。

When I thought about it, it all came back.

當我回想起來，往事全都涌上了心頭。

重新流行;再度時興

I'm glad hats are coming back.

我很高興又開始流行戴帽子了。