HSK 7-9
川流不息
chuānliú-bùxīthe stream flows without stopping (idiom); unending flow
街上车辆终日川流不息。
Jiē shàng chē liàng zhōng rì chuān liú bù xī.
Vehicles flow endlessly along the street all day.
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Appears across levels (7-9) in the HSK 3.0 word list.