A, B, D
If you take selection D to mean any multiple of Equation 1 added to any (possibly different) multiple of Equation 2, then that selection includes the cases described in selections A and B.
As long as the properties of equality are observed, and the operations performed are reversible (can be undone to give the original equations), those operations are allowed.
Appropriate selections are A, B, D.
_____
Comment on this question
These transformations form the basis for methods of solution of systems of linear equations.