The signal for a fire emergency on an OSV is（）.
A. a 30 second on 30 second off alternating signal
B. the continuous blast of the ships whistle for not less than 10 seconds supplemented by the continuous ringing of the general alarm bells for not less than 10 seconds
C. an intermittent ringing of the general alarm for not less than ten seconds
D. announced over the PA system
微信支付 
支付宝支付