根据句意,补全对话。
— What are the students ____?
— They are ____ for their parents.
读下图,回答下列小题。
冬天,牙医常把检查口腔的金属小镜子放在酒精灯上烤一烤后才伸进口腔内进行检查.这样做的主要目的是