The transmission time duration of a single pulse of radio-frequency energy is a function of the（）.

A.Relative
B.TRUE
C.Compass
D.Magnetic

A.magnetism from the earth's magnetic field
B.misalignment of the compass
C.magnetism within the vessel
D.a dirty compass housing

A.deviation minus variation
B.variation plus compass course
C.combined variation and deviation
D.difference between true and magnetic heading