识别危险因素可以从（）等方面进行。
A.人
B.物和环境
C.人、物、环境的匹配
D.规章制度的完善健全
E.安全管理状况
参考答案：C, E
The figure above is a regular hexagon with center H, The shaded area is a parallelogram that shares three vertices with the hexagon; its fourth vertex is the center of the hexagon. If the length of one side of the hexagon is 8 centimeters, what is the area of the unshaded region ？（）
A.A
B.B
C.C
D.D
E.E
人胚早期发生是指（）周的发育。
