不要冒充警察，这是违法行为。

bùyào màochōng jǐngchá, zhè shì wéifǎ xíngwéi.

Don't pretend to be a police officer; this is illegal behavior.

他试图冒充公司高层的高级经理。

tā shìtú màochōng gōngsī gāocéng de gāojí jīnglǐ.

He tried to impersonate a senior manager in the company's top management.

他在网上冒充医生，给别人乱开药，特别危险。

Tā zài wǎngshàng màochōng yīshēng, gěi biéren luàn kāi yào, tèbié wēixiǎn.

He pretended to be a doctor online and randomly prescribed medicine to others, which was extremely dangerous.