wǒ / tīng / dào / yào / shi / zhuǎn / dòng / de / kǎ / da / shēng / zhī / dào / mā / ma / huí / lái / le

我听到钥匙转动的咔哒声，知道妈妈回来了。

I heard the click of a key turning and knew that Mom had come home.