笼养蛋鸡疲劳综合症的病因不包括（）

A.缺乏运动

B.维生素B缺乏

C.维生素D缺乏

D.饲料中钙缺乏

E.钙磷比例不当

_____earth scientists understand how and why earthquakes happen, forecasts are usually inaccurate.[ ]

A. As

B. While

C. Because

D. If