单项选择题
A.stop your engines
B.sound two prolonged blasts of the whistle
C.sound the danger signal
D.slow to bare steerageway
单项选择题 You are underway at 5 knots and see on your radar a contact 10 miles directly astern of you. 12 minutes later，the contact is 8 miles directly astern of you. What is the estimated speed of the contact? （）
单项选择题 You are scanning the radar screen for a buoy fitted with racon. How should this signal appear on the PPI display?（）
单项选择题 Which statement is true concerning a vessel equipped with operational radar?（）.