spend有兩種用法：
1、主語(yǔ) + spend + 時(shí)間/錢(qián) + on something.
例：I spent 4 yuan on the book.
2、主語(yǔ) + spend + 時(shí)間/錢(qián) + in doing something(“in”可以省略）.
例：She spent 14 dollars (in) buying this pair of shoes.
pay有一種不同的用法：
pay + 錢(qián) + for sth.
例：He paid 90 pounds for the chair.