什么是自然坡面？
参考答案：
自然坡面：翻卸货物在上部平盘与下部平盘间自然堆存形成的坡面。
唐蕃正式结盟是在 [ ]
A．唐太宗时
B．唐高宗时
C．唐玄宗时
D．唐中宗时
A number of students_____ playing on the ground but I don't know what the exact number______.
[ ]
A. are; is
B. are; are
C. is; is
D. is; are
