单项选择题
A.plug the vents
B.plug the sounding pipes
C.plug the scuppers
D.close the lids on the vents
单项选择题 A position that is obtained by using two or more intersecting lines of position taken at nearly the same time，is a(n) （）.
单项选择题 A position that is obtained by applying estimated current and wind to your vessel’s course and speed is a(n) （）.
单项选择题 A position obtained by crossing lines of position taken at different times and advanced to a common time is a(n) （）.