在房子上乱涂乱画是非法的。

It's illegal to deface property.

《柯林斯英汉双解大词典》

售香烟给未到法定年龄的儿童是非法的。

It is illegal to sell cigarettes to children who are under age.

《牛津词典》

在街头兑换货币是非法的–始终要去银行。

Changing money on the street is illegal – always use a bank.

《柯林斯英汉双解大词典》

And keep in mind when Crane wrote those lines too, it was illegal to buy and sell wine in this country.

记住克莱恩写下这些诗句的时候，禁酒令还在适用，买卖酒都是非法的。

耶鲁公开课 - 现代诗歌课程节选

So we worked on people being held unlawfully in Afghanistan by the U.S. military.

我们打交道的是那些在阿富汗被美国军队非法扣押的人。

在哪都可以实习 - SpeakingMax英语口语达人

Those people are all in trouble because it's illegal to trade on insider information and they tracked them all down.

所有人都惹上了麻烦,因为内幕交易是非法行为,全部人都被捕了

耶鲁公开课 - 金融市场课程节选