有些东西可以一个一个数：one apple, two apples。另一些我们通常不会单独去数：water, rice, bread。快速判断：在它前面加 one, two, three 数数看，听起来自然吗？
能数吗？
one apple, two apples (you count them one by one)
water (we do not say "two waters" for the water itself)
one chair, two chairs (you count them one by one)
试一试: Which one do you count one by one (one, two, three)? (a book / rice / water) 答案: a book — 如果你选了 rice 或 water，这些我们不会单独去数：“two rices”和“two waters”听起来都不对。books 可以一本一本数：one book, two books。
不可数：不加 a，不加复数
遇到不能数的东西，不用 a / an，也不加 -s。改用 some，或者什么都不加，直接用这个词。
I drink water every day.
Would you like some coffee?
She gave me some advice.
Not "I want a water." — say "I want some water.". 水是数不了的，所以这里不加 a。用 some water（或者 a glass of water）。
试一试: There is ___ on the table. (some bread / a bread / two breads) 答案: some bread — 面包没法一个一个数，所以不能说 "a bread"，也不能说 "breads"。用 some bread（或者 a piece of bread）。
要慢慢习惯的常见词
有几个日常用词其实不能数，虽然感觉上好像可以。多练习就会习惯这些词：money, time, bread, rice, water, homework, advice。
I need some money. (not "a money")
She gave me good advice. (not "an advice")
I have homework tonight. (not "a homework")
试一试: Mei gave me ___ before the test. (some advice / an advice / some advices) 答案: some advice — "Advice" 就是这种不能数的词：不能说 "an advice"，也不能说 "advices"。用 some advice。（这些常见词多练习就会习惯。）
用容器来数它们
那 water 怎么数呢？数装它的容器：a glass of, a cup of, a piece of。这时数字加在容器上：two glasses of water，而不是“two waters”。
a glass of water, two glasses of water
a cup of coffee
a piece of bread
试一试: Camila asked for ___ with her meal. (a glass of water / a water / two waters) 答案: a glass of water — “A water”和“two waters”是在数水本身。改成数装水的容器：a glass of water。
试一试: Can you count it? Hiroshi needs ___ for the trip. (some money / a money / two moneys) 答案: some money — 钱没法一个一个数（不能说 "a money"，也不能说 "moneys"），所以用 some money。（数不了的东西，就用 some 或者容器。）