單項選擇題An indirect radar echo is caused by a reflection of the main lobe of the radar beam off the observer’s vessel. Which of the following is NOT a characteristic of indirect echoes?（）.

A.Their bearing is almost constant，even when the true bearing of the contact changes appreciably
B.They always appear on a bearing of 90°from the true bearing of the contact
C.The indirect echoes usually appear in shadow sectors
D.When plotted，their movements are usually abnormal


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1.單項選擇題An electronic depth finder operates on the principle that（）.

A.radio signals reflect from a solid surface
B.sound waves travel at a constant speed through water
C.radar signals travel at a constant speed through water
D.pressure increases with depth

2.單項選擇題An ECDIS is required to display which information?（）

A.Water temperature
B.Climatology data
C.Speed of advance
D.Depth contours

3.單項選擇題An ECDIS is required to display which information?（）

A.Soundings
B.Waypoints
C.Meteorological data
D.Radar targets

4.單項選擇題An ECDIS is required to display which information?（）

A.Radar targets
B.ARPA vectors
C.Hydrographic data
D.All of the above