flap

The sails flapped in the breeze..风帆在微风中摆动。

the flap of the sails.船帆的拍动

The wings of the bird still ______ after it had been shot down.句意： 鸟被射落后， 翅膀仍在拍动。slap： 拍击， 掌击； scratch： 抓， 擦伤； fluctuate： 波动， 动摇。314fluctuated

skin flap,皮瓣

pocket flap,袋盖

valve flap,阀瓣

flap gate,铰链式闸门；舌瓣闸门；翻转板

flap valve,瓣阀；片状阀

flap wheel,翼片砂轮