How does the insertion take place?

You want to insert an operatio at a certain time on work center. The planning direction is forward. The disired dispatching time concides with an operation that has previously been dispatched .

How does the insertion take place?
A . The previously dispatched operation stays as is; the new operation is inserted after the the dispatched operation.
B. The previously dispatched operation stays as is; the new operation is inserted before the the dispatched operation.
C. The new operation is inserted at the desired time; the previously dispatched operation is moved forward.
D. The new operation is inserted at the desired time; the previously dispatched operation is moved backward.

Answer: D