spend的主语必须是人,常用于以下结构：
(1) spend time ／money on sth.在……上花费时间（金钱）.例：I spent two hours on this problem.这道题花了我两个小时.
(2) spend time ／ money (in) doing sth.花费时间（金钱）做某事.例：They spent two hours finishing doing homework.他们花了两个小时做作业.
cost的主语是物或某种活动,常见用法如下：(1)sth.costs sb.Some money,某物花了某人多少钱.例：A new computer costs me a lot of money.买一台新电脑花了我一大笔钱.
(2) doing sth.costs sb.Some time ,做某事花了某人多少时间.例：Remembering these new words cost him a lot of time.他花了大量时间才记住了这些单词.Take一般用it做形式主语,常见用法有以下几种：(1) It takes sb.Some time to do sth.做某事花了某人多少时间.例：It takes about 10 minutes.花费了10分钟
Pay主语是人,有很多种用法：(1) sb.pay some money for sth.某人为某物付款.例如：I paid 5 dollars for the book.
哎,字好多啊