The bottle cap keeps the water in.

瓶盖让瓶里的水不流出来。

youdao

There is a film of mould over the bottle cap.

瓶盖上有一层薄薄的霉菌。

《新英汉大辞典》

The bottle cap popped off and he got an eyeful of Seltzer.

瓶盖砰地一声打开，喷得他满眼都是矿泉水。

《新英汉大辞典》

"It's so simple. With a two-liter bottle you add sugar, you add extract, you add a small amount of yeast and water, cap it up and in two days they've got root beer.

VOA: special.2011.08.01

An exhibition of handmade vote boxes or bottle cap sculptures was an opportunity to discover educational and entertaining activities organized within and outside the school.

UNESCO: THEMES

Only interested in the bottle-cap business, Crown sold off the insulation part of Mundet just 93 days later.

FORBES: An Affair to Remember

The company contended that it only bought Mundet's bottle-cap assets and that merely buying assets isn't a merger and doesn't trigger liability.

FORBES: An Affair to Remember