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

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

出自：海船船员证

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