用恰当的单词填空完成表格。
College students volunteer in the US
In ____
They ____books to the sick people or listen to their problems.
In old people's homes
They help to clean up or go ____.
In the ____clubs
They remember the problems of boys and girls
在下列条件下，让置于密闭容器中的下列各组物质充分反应后，再冷却至常温，密闭容器中的气态物质属于纯净物的是（）
