棱长为1的正四面体,某顶点到其相对面的距离为 .
正面体重,顶点到相对面的射影为该面等边三角形的重心。因为棱长为1,所以射影到等边三角形的顶点距离为,所以顶点到相对面的距离
治疗风湿顽痹及顽固性头痛,最宜选()
A.藁本
B.钩藤
C.羌活
D.僵蚕
E.蜈蚣
- Where is Eric? I can’t find him anywhere.
-He _______ the library. You can find him there. [ ]
A. was away from
B. has left
C. has been to
D. has gone to