如果两个不在同一直线上的分运动都是匀速直线运动，对其合运动的描述中，正确的是

A．合运动一定是曲线运动

B．合运动一定是直线运动

C．合运动是曲线运动或直线运动

D．当两个分运动的速度数值相等时，合运动为直线运动

From the deep valley ______, which had my heart in my mouth.

A．came a frightening sound

B．a frightening sound came there

C．did a frightening sound come

D．a frightening sound did come