单项选择题
A.at all times
B.in the bottom return mode
C.in the volume reverberation mode
D.only when there is no current
单项选择题 A disadvantage of using chain lashing on heavy vehicles aboard Ro-Ro vessels is that it is （）.
单项选择题 A device fitted over the discharge opening on a relief valve consisting of one or two woven wire fabrics is called a flame（）.
单项选择题 A decrease in barometric pressure is associated with all of the following except（）.