对于做平抛运动的物体，不计空气阻气，g为已知，下列条件中可确定做平抛运动物体的飞行时间的是     (    )

A．已知物体的水平速度

B．已知下落的高度

C．已知物体的水平位移

D．已知物体的竖直速度

According to Halliday, a British linguist, social context of language can be analyzed in terms of three factors :______ of discourse

A．the range, length and content

B．the situation, context and mode

C．the field, tenor and mode

D．the context, content and field