在以下几个单位中,反映声音的高低的单位是[ ]
A. Hz
B. m/s
C. dB
D. s
答案:C
—I think art is very interesting.
—_________.Music is more interesting than art.[ ]
A. I disagree
B. I think so
C. I agree
D. I don't know
高千伏摄影特点的叙述,正确的是()
A.获得层次丰富的X线照片
B.缩短曝光时间,减少被照体移动模糊
C.减少管电流,延长X线管寿命
D.散射线减少,照片对比度较高
E.有利于病人防护