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     Hi, I'm John.There are four seasons in a year. I like them all. In spring, it's warm. There are pretty flowers everywhere. I often go on a picnic with my parents. Summer is hot. I often go swimming in the pool. I like to wear my sunglasses. In fall, the weather is cool. I can help my grandpa pick apples. Winter is white. I can make a snowman. And I can go skating, too.

小明同学是学校环境保护课外活动小组成员，在一次对周边水污染情况的调查中，他对污水的密度进行了测量．其探究步骤如下：

用调节好的天平测出玻璃杯和污水的总质量为139g

①孔子     ②孟子    ③孙武

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