每个钢柱主角钢下钢垫片数不得大于（）片。
A.2
B.3
C.4
D.5
参考答案：B
No navigational aids are shown and chart is not kept（）for alterations in depths inside the pecked lines joining Hurst pt. to Warden pt.
A.accurate
B.correct
C.corrected
D.accuracy
肾锥体为（）
A.强回声
B.等回声
C.低回声
D.较低回声
E.无回声
