A large vessel is equipped with a controllable pitch propeller. Which statement is TRUE?（）.

A.When dead in the water，it is often difficult to find the neutral position and slight headway or sternway may result
B.When going directly from full ahead to full astern，there is complete steering control
C.When the vessel has headway and the propeller is in neutral，there is no effect on rudder control
D.When maneuvering in port，full ahead or astern power can usually be obtained without changing shaft RPM