下列物质长期敞口放置在空气中，质量增加而不变质的是（　　）

如图是某同学设计的一组实验：在两个大小几乎相同的萝卜中各挖一个大小相等的洞，向甲、乙萝卜的洞中分别注入等量的清水和浓盐水，各用一个装有玻璃管的橡皮塞塞住洞口，记下玻璃管内液面的高度．放置一段时间，分析出现的变化：

    It's Sunday morning. There are many people in the park, some boys are playing basketball. There are some girls under a big tree. They're singing and dancing. What are those women doing? They are drinking tea. Look at the woman in a blue coat. Who's she? She's my mother. She is talking to Edward. Edward is her student. He is a good student. He studies hard. He's good at all the subjects. And he's friendly to all his teachers and his friends.