1、definite

明确的;确定的

It's too soon to give a definite answer.

要给出一个明确的答复，现在还为时过早。

Her Royal Highness has definite views about most things.

女王陛下对大多数事情都有明确的观点。

(证据或信息)确凿的，确切的

We didn't have any definite proof.

我们没有任何确实的证据。

If you have any definite news of my husband, please let me know.

如果有我丈夫的确切消息，请一定告诉我。

清楚的;明显的;无疑的

There has already been a definite improvement.

已经有了显著的改进。

That's a very definite possibility.

那是很有可能的。

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。