试件表面为中等粗糙，但要求检测灵敏度较高，应选用哪种型式的渗透探伤材料较佳？（）
A、水洗型
B、后乳化型
C、溶剂型
D、以上都可以
参考答案：B
土球上部复土厚度不超过土球高度的（）
A、10%
B、20%
C、30%
D、40%
How does an icebreaker normally free a ship which has become beset while navigating independently?（）
A.By backing down the track and cutting out ice on either bow
B.By approaching from the stern and crossing ahead at an angle of 20° to 30° to the beset ship's course
C.By overtaking the beset ship，running ahead and then backing down the track to the beset vessel
D.By approaching the vessel from astern and towing the beset vessel stern first
