心脏里的瓣膜帮助控制血液流动的方向。

The ___valves in the heart help control blood flow direction.

工程师正在检查暖气系统的阀门是否正常工作。

The engineer is checking if the ___valves in the heating system are working properly.

小号手需要经常清洁保养乐器上的阀门。

The trumpet player needs to regularly clean and maintain the ___valves on the instrument.