A principal vector  and principal moment  can be obtained by reducing an inertial force system to one point (reduction center). Which statements are correct?

A． The principal moment  depends on the position of the reduction center.
B． The principal moment  doesn’t depend on the position of the reduction center.
C．The principal vector  depends on the position of the reduction center.
D．The principal vector  doesn’t depend on the position of the reduction center.