Answer
A, C
Work Step by Step
The indirect method is good when there is a broad scenario, for you only have to prove one time that it does not make sense to prove it incorrect. In case A, all we have to do is to show that it would be absurd for them to be equal, so the indirect method works. However, in case B, to prove that the angles are exactly the same is a specific case, so the indirect method would not be good. Case C is similar to case A, so the indirect method is also good for C. Case D is similar to B, so the indirect method is not good for case D.
