单项选择题
A.15 minutes without recharging
B.20 minutes without recharging
C.25 minutes without recharging
D.30 minutes without recharging
单项选择题 Cable tension for catenary calculations is taken at the（）.
单项选择题 By regulation，life preservers aboard an uninspected towing vessel must be（）.
单项选择题 As you hold a piece of manila line vertically in front of you，the strands run from the lower left to the upper right. Which type of line is this?（）