C语言规定标识符只能由_____、_____和下划线3种字符组成，且第一个字符必须为_____或下划线。
参考答案：字母数字字母
My sister would rather ______ at home reading books than ______ on National Day. [ ]
A. to stay; to travel
B. stay; travel
C. stay; traveling
D. stayed; traveled
食管内扁圆形异物，在正位上呈冠状面，侧位上呈矢状面排列。气管内异物与之相反。
