1、come back

回忆起;回想起来

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

他当时也是一位国会议员，他的名字我得想一下才能记起来。

When I thought about it, it all came back.

当我回想起来，往事全都涌上了心头。

重新流行;再度时兴

I'm glad hats are coming back.

我很高兴又开始流行戴帽子了。

2、necessary

必要的;必需的

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

我没让发动机熄火，因为也许需要迅速离开。

We will do whatever is necessary to stop them.

我们要采取一切必要措施去阻止他们。

(结果或联系)必然的，势必的

Wastage was no doubt a necessary consequence of war.

巨大的损耗无疑是战争的必然结果。

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

科学工作与艺术的区别在于它与人类进步有着必然联系。

如果必要的话

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

必要时，飞艇能在那里停留数天以躲避危险。

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

军队需要在必要时愿意投入战斗的军人。