This is my school. There are many trees and flowers in it. The teaching building is big and tall. There is a big playground in our school. After 4:30 in the afternoon, many students come to the playground to play football and some students play table tennis in the table tennis room.
There are 1,200 students in 25 classes in our school. The students all like to study. The teachers in our school are very good. They help the students to study and the students like them, too.

历史上贝壳、牲畜、布匹等都曾充当过商品交换的媒介,但随着商品交换的发展,“贵金属”长期占据货币的宝座。下面对此认识正确的是（  ）

①“贵金属”是充当一般等价物的唯一商品　②货币是商品交换发展到一定历史阶段的产物　③“贵金属”固定地充当一般等价物时,货币产生　④所有充当过商品交换媒介的商品都是货币的替代物

浪费可耻，“光盘”行为光荣，同时食品安全也越来越被人们关注，下列生活中常见的行为或做法，不合理的是（  ）