juice是汁的意思，而fruit juice则是果汁的意思，区别可以从以下例子看出：
I like food with some juice, and I also like fruit juice, such as apple juice or orange juice, as they are full of vitamins. 我喜欢有汁的食物，我也喜欢果汁，比如苹果汁或橙汁，因为它们富含维生素。
juice除了果汁还可以表示蔬菜汁；肉汁；胃液；消化液。
fruit juice只表示果汁。
