单项选择题
A.heavy rain within six hours
B.a decrease in wind velocity
C.a change in the present weather conditions
D.that fog will soon set in
单项选择题 A radar range to a small，charted object such as a light will provide a line of position in which form? （）
单项选择题 A quick and rapid motion of a ship in a seaway is an indication of a(n) （）.
单项选择题 A pumproom is suspected of accumulating gases after a ventilation machinery breakdown. Where should the combustible gas indicator case be placed when testing the pumproom atmosphere for combustible gases? （）