看到这么感人的场景，他不由得流下了眼泪。

Kàndào zhème gǎnrén de chǎngjǐng, tā bùyóude liú xiàle yǎnlèi.

Seeing such a touching scene, he couldn't help but shed tears.

这个笑话太搞笑了，听了不由得大笑起来。

Zhège xiàohuà tài gǎoxiào le, tīngle bùyóude dàxiào qǐlái.

This joke is so funny that you can't help but burst into laughter.

面对这么艰难的局面，他不由得感到一阵无助。

Miàn duì zhème jiānnán de júmiàn, tā bùyóude gǎndào yī zhèn wúzhù.

Faced with such a difficult situation, he couldn't help but feel helpless.