Please help with this asap thanks :) Question: What reason can be used to complete this proof?

m∠1=m∠3 because ∠1≅∠3.
m∠1+m∠2=m∠CXB and m∠2+m∠3=m∠AXD .
m∠1+m∠2=m∠AXD because you can substitute m∠1 for m∠3.
m∠CXB=m∠AXD by the transitive property of equality.
So, ∠AXD≅∠CXB.

Answers:
A: because that is given information

B: by the angle addition postulate

C: because you can measure them with a protractor

D: because m∠CXB=m∠AXD