Colours can change our moods and make us happy or sad, energetic or sleepy.
《神奇的极光》首先列举了有关极光的东西方传说。说明极光存在的____,再诠释极光的定义,介绍极光的____。
如图所示,液态的蜡凝固时体积缩小,中间凹陷,对此现象分析错误的是