下雨天，他的膝盖总是隐隐作痛。

Xiàyǔtiān, tā de xīgài zǒngshì yǐnyǐn zuòtòng.

On rainy days, his knees always ache dully.

他跑步时不小心摔倒，膝盖都擦破了。

Tā pǎobù shí bù xiǎoxīn shuāidǎo, xīgài dōu cāpò le.

He accidentally fell while running and scraped both his knees.