单项选择题
A system of reservoirs and connecting tubes in a gyro compass is called a（）.
A.spider element B.mercury ballistic C.gyrotron D.rotor
单项选择题 A single vertical magnet placed underneath the compass in the binnacle is used to compensate for（）.
单项选择题 A compass card without north-seeking capability that is used for relative bearings is a(n)（）.
单项选择题 （）is on the panel of DF.
