number of + 可数名词 例句： A large number of cows were infected. There are a number of reasons why I can’t marry you. A number of people were injured in the explosion. I had warned her not to go there any number of times, but she wouldn’t listen.
amount of +不可数名词 例句： The amount of work I got through in July was double the amount that I did in June. No amount of love would heal the hatred she felt. I had a certain amount of respect for him: he was a good footballer and a good ambassador for his country.
quantity of （或quantities of）+一般接无生命的名词，可数不可数皆可，更加正式。 例句： They have recovered a quantity of petrol bombs at Wolff Close. There were very small quantities of peppers on sale in the market. There are very large quantities of gas beneath the North Sea.
