单项选择题
AREAS WHICH CANNOT BE SCANNED BY THE RADAR OF THE VESSEL BECAUSE THEY ARE SHIELDED BY PARTS OF ITS SUPERSTRUCTURE，MASTS，ETC means（）.
A.Blind sectors
B.Sheltered area
C.Unseen area
D.Unscanable area
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相关考题
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单项选择题
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 -
单项选择题
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 -
单项选择题
An ECDIS is required to display which information?（）
A.Water temperature
B.Climatology data
C.Speed of advance
D.Depth contours
