我弟弟今年二十一岁了。

My younger brother is ___twenty-one years old now.

他在赌场里玩二十一点赢了不少钱。

He won a lot of money playing ___twenty-one at the casino.

在美国，年满21岁才可以合法饮酒。

In the US, you must be ___twenty-one to drink alcohol legally.