Using the unit-load method to calculate the displacement of statically indeterminate structures. Which of the following conclusions is correct? ( )

A、Theunitloadcanonlybeaddedtothecorrespondingprimarystructure.;
B、Theunitloadcanonlybeaddedtotheoriginalstaticallyindeterminatestructure.;
C、TheUnitloadcanbeaddedtothecorrespondingequivalentsystem.;
D、Unitloadcanbeaddedtotheoriginalstaticallyindeterminatestructureorthecorrespondingprimarystructure.