■ potato

作为类别的总称，对之加以说明，要用加定冠词的单数，说 the potato。

• The Atkins diet was the rage, and prospects for the potato were dim.阿特金斯膳食法当时正在大行其道，土豆的前景就很黯淡。

但是如果不是笼统的总称，而是参与某一过程的“土豆”（只是一些土豆），就用复数 potatoes（不用 the），此时 potatoes 实际上是个不可数的物质名词，类似 eggs, oats 之类，甚至前面可以用 much。

• There is three times as much potatoes and two times as much carrots as beef.土豆是牛肉的三倍，胡萝卜是牛肉的两倍。

但是无 the 的复数 potatoes 也可以用作泛指，仍然是参与某一过程，而不是概括总类。

• Vodka was first made with potatoes.烧酒最初是用土豆制作的。
• Now, about 350 million tons are grown each year, making potatoes the fourth-largest source of food on the planet behind rice, wheat, and corn. (US News & World Report, Feb. 18, 2008, p.34)现在每年种出的土豆有三亿五千万吨，使得土豆成了仅次于大米、小麦、玉米之后的第四种最大的食料。

tomato 的搭配用法也与此相似。