spend 后既可接时间又可接钱,如：
I spend two hours on my homework．或 I spend two hours
in doing homework．
I spend 100 dollars on the coat．
cost后只能接钱,如：
It costs me much money to buy the books.
take 后只接时间,如：
It takes her 3 hours to finish her homework.
注意cost 和 take 不能用人做主语．
plenty of后只接不可数名词,a lot of后既接可数又能接不可数名词．