3 sentences

1. 车主必须购买第三者责任险。

   chē​zhǔ bì​xū gòu​mǎi dì​sān​zhě zé​rèn​xiǎn.

   Car owners must purchase third-party liability insurance.

   Source: Dong Chinese Dictionary

2. 在列出的三项提议中，第三者最难实现。

   zài liè​chū de sān xiàng tí​yì zhōng, dì​sān​zhě zuì nán shí​xiàn.

   Among the three proposals listed, the third one is the most difficult to achieve.

   Source: Dong Chinese Dictionary

3. 由于第三者的介入，他们的婚姻最终走向了破裂。

   yóu​yú dì​sān​zhě de jiè​rù, tā​men de hūn​yīn zuì​zhōng zǒu​xiàng le pò​liè.

   Their marriage eventually broke up due to the involvement of a third party.

   Source: Dong Chinese Dictionary