调幅波的频带宽度B与调制信号频谱FMIN-FMAX的关系为()
A、B=2FMIN
B、B=2FMAX
C、B=FMIN
D、B=FMAX
参考答案:B
Don’t worry about Mary. _______ , she is no longer a child any more.
A.At all
B.After all
C.In all
D.Above all
塔吊停用时起重小车要收回、松开旋转制动器,小车置于(),吊钩升到离起重臂顶端2~3m处
A.非工作状态
B.塔臂中部
C.塔臂后端
D.塔臂前端