--- Do you take exercise every day?
----Yes. I always______ thirty minutes after supper.

动词辨析 spend 人做主语，spend+钱或时间+on something/in doing sth; cost物作主语，花钱； take一般用it takes sb. 一段时间 for sb. to do sth; pay 人做主语，一般用pay for 表示付钱。

对四个花费“pay,spend,cost, take"的用法不熟悉而出现错误。