I can take the car if necessary.

如果必要的话，我可以乘汽车去。

《牛津词典》

If necessary I can come at once.

如果有必要，我可以马上来。

《牛津词典》

If necessary , you can contact me at home.

必要的话，我在家时你也可以和我联系。

《牛津词典》

He used strong language and seemed to say that the United States would fight, if necessary,to defend its claim.

VOA: special.2009.02.19

In very severe cases, it can even defile some common objects, and in those cases, the source of impurity might have to be isolated or excluded if necessary.

在一些非常严峻的情况中，它会玷污一些普通的事物，在这种时候，不洁之源,也许只能被孤立，严重的话需要驱逐。

耶鲁公开课 - 旧约导论课程节选

We're going to get a deep insight if it's a necessary truth about death that everyone dies alone.

如果这是对死亡来说必不可少的真理,那我们能得到一些深刻理解。

耶鲁公开课 - 死亡课程节选

He made a wisecrack about dealing with deflation, if necessary, by dropping dollar bills from aircraft.

FORBES: The Bupkes Bond

We should have boarded the vessel on the high seas and, if necessary, confiscated its cargo.

FORBES: How to Stop North Korea

Comments can be gathered after the rule goes into effect and the rule tweaked, if necessary.

FORBES: FAA Foot-Dragging on Rule to Prohibit Texting and Flying