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?（）

A.Starting with a dash and extending radially outward from the target
B.As a broken line from center of PPI to the target
C.Starting with a dot and extending radially inward from the target
D.Starting with a dash and extending to the right of the target

单项选择题Which statement is true concerning a vessel equipped with operational radar?（）.

A.The Master of the vessel must be on the bridge when the radar is in use
B.The radar equipment is only required to be used in restricted visibility
C.The use of a radar excuses a vessel from the need of a look-out
D.This equipment must be used to obtain early warning of risk of collision

单项选择题Which statement is TRUE concerning a vessel equipped with operational radar?（）.

A.She must use this equipment to obtain early warning of risk of collision
B.The use of a radar excuses a vessel from the need of a look-out
C.The radar equipment is only required to be used in restricted visibility
D.The safe speed of such a vessel will likely be greater than that of vessels without radar

单项选择题Which statement concerning the operation of radar in fog is TRUE?（）

A.Radar ranges are less accurate in fog
B.Navigation buoys will always show up on radar
C.A sandy beach will show up clearer on radar than a rocky cliff
D.Small wooden boats may not show up on radar

单项选择题Which statement about an estimated position is TRUE?（）

A.It is more reliable than a fix based on radar bearings
B.It may be based on a single LOP or questionable data
C.When a 3-LOP fix plots in a triangle，the center of the triangle is the estimated position
D.It is usually based on soundings