1 sentence

1. 由于光线突然变暗，他的瞳孔不由自主地放大了。

   yóu​yú guāng​xiàn tū​rán biàn àn, tā de tóng kǒng bù​yóu​zì​zhǔ dì fàng​dà le.

   His pupils dilated involuntarily as the light suddenly dimmed.

   Source: Dong Chinese Dictionary