（1）The carbohydrates, proteins, and fats in food are broken into simpler forms in the digestive tract. (TOEFL)
(2) Pickling of foods began in prehistoric times. (TOEFL)
food 为不可数名词,因此,在句(1)中,food 以单数形式出现是正确的。但是在句(2)中,为什么出现了 food 的复数形式 foods 呢?
大家都知道,物质名词(material nouns)属不可数名词(noncount nouns 或 uncountable nouns),因此一般总是用作单数:food, paper, water, steel, tea, coffee, fruit。
但是,当需要强调不同的种类时,有些物质名词就需要采用其复数形式:foods, wines, teas, steels, coffees, fruits。
请看下面的例句：
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Too many sweet foods, like cakes and pastry, may increase your weight. (LDCE) 吃太多的甜食，例如蛋糕和酥饼会增加体重。
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He wrote out a long list of all the foods which were forbidden. (New Concept English Book 2, L. 51) 他列出一张禁食的长单子。
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The sad truth is that most of us have been brought up to eat certain foods and we stick to them all our lives. (New Concept English, Book 3, L. 23) 最糟的事情是: 我们大部分人都是在吃某些固定的食品中长大的, 而且一辈子都专门吃这些东西。
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There were all kinds of foods to eat, including wild birds, such as ducks, geese and turkeys. (VOA) 有各种各样的食物，包括野鸭、野鹅和火鸡等野味。
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Greece has some wonderful fruits. (Mis) 希腊有一些非常好吃的水果。
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This dish is made from a mixture of four different summer fruits. (LDCE) 这盘菜是由四种不同的夏季水果混合而成。
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We stocked a wide range of inexpensive wines. (Chambers) 我们贮存了各种各样廉价的酒。
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This hotel serves teas. (ELD) 这家旅馆用各种茶招待客人。
They are needed for ____ foods into energy and body maintenance.