1、definite

明確的;確定的

It's too soon to give a definite answer.

要給出一個明確的答復，現在還為時過早。

Her Royal Highness has definite views about most things.

女王陛下對大多數事情都有明確的觀點。

(證據或信息)確鑿的，確切的

We didn't have any definite proof.

我們沒有任何確實的證據。

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

如果有我丈夫的確切消息，請一定告訴我。

清楚的;明顯的;無疑的

There has already been a definite improvement.

已經有了顯著的改進。

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。