hundred of 、thousand of、million of 、billion of 如果运用在句子中,要不要加“s”呢
eg:there are hundreds of people 这里hundred 加了s 但名词没加s
i have a couple of thousand pounds in the bank.i can afford the precious piano.这里thousand没有加s但后面的名词加了s
Thousands of letters are never delivered because the addresses are incorrect.这里的thousand和 letter都加了s
能说说为什么吗