英语问题I spent 5 dollars on the book这里的spend为什么要变成spent

英语问题I spent 5 dollars on the book这里的spend为什么要变成spent l spent 5 dollars on that book.l_____5 dollars_____that book I spent two hours on my homework一句中spend为什么要用过去式spent I spent ten dollars on the picture 同义句 I spent 100 dollars on the dress yesterday 的同意句 I spent ten dollars on the picture 同义句 I ten dollars the pic “He spent 2 hours playing the piano.”中为什么用“spend”的过去式“spent” I spent fifteen yuan on this book. I spent forty dollars on the jeans.(同义句) the jeans_____ ____ I __ twenty dollars on the coat.A paid B spent C gave D cost This is the ring on which she spent 1000 dollars. I spent ten yuan on the book.I ____ten yuan ____the book.改为同