烟雾信号是发烟的视觉信号，晚上、白天都可使用。（）
参考答案：错
Scientists have advanced many theories about why human beings cry tears , none of （） has been proved.
A. whom
B. which
C. what
D. that
膀胱刺激征为( )
A．尿频、血尿B．尿急、脓尿C．尿痛、排尿困难D．血尿、脓尿、尿频E．尿频、尿急、尿痛
