Their bearing is almost constant，even when the true bearing of the contact changes appreciably
They always appear on a bearing of 90°from the true bearing of the contact
The indirect echoes usually appear in shadow sectors
When plotted，their movements are usually abnormal
第1题：
在UNIX系统中，Shell程序(21)实现显示用户主目录以及当前命令的进程标识符。
A．echo UserHome directory:$LOGNAME echo Current shell's PID:$$
B．echo UserHome directory:$HOME echo Current shell'PID:$@
C．echO UserHOme directOIy:$LOGNAME echo Current shell'sPID:$@
D．echo UserHome directory:$HOME echo Current shell'sPID:$$
第2题：
A. Client ID
B. Cluster list
C. Originator ID
D. Reflection community
第3题：
Radar reflectors are required for ______.
A.all fishing vessels over 39 feet in length
B.sail-propelled fishing vessels
C.all fishing vessels of less than 200 GT
D.wooden hull fishing vessels with a poor radar echo
第4题：
A combination of corrosion and erosion caused wastage in the main ballast line，which directly led to the leak ______．
A.draff
B.wastage
C.mullock
D.obsolete
第5题：
The description Racon beside an illustration on a chart would mean a ______.
A.radar conspicuous beacon
B.circular radiobeacon
C.radar transponder beacon
D.radar calibration beacon
第6题：
显示用户的主目录的命令是什么（）
A.echo$HOME
B.echo$USERDIR
C.echo$ECHO
D.echo$ENV
第7题：
My radar is not working．I require shorebased radar assistance．Is shorebased radar assistance ________ ？
A.used
B.available
C.in use
D.can be used
第8题：
The radar control that shortens all echoes on the display and reduces clutter caused by rain or snow is the ______.
A.sensitivity time control (sea clutter control)
B.receiver gain control
C.brilliance control
D.fast time constant (differentiator)
第9题：
The Insurance Company shall be liable for ______.
A.loss or damage caused by unseaworthiness of the insured ship
B.demurrage of the insured ship and other indirect expenses
C.reasonable expenses for ascertaining the loss or damage within the scope of Cover
D.A，B，C are all wrong
第10题：
You have another ship overtaking you close aboard to starboard．You have 3 radar targets bearing 090° relative at ranges of 0.5 mile，1 mile，and 1.5 miles．In this case，the unwanted echoes are called ______．
A.Multiple echoes
B.Spoking
C.Indirect echoes
D.Side-lobe echoes