Hey there!
Here is the answer to your question.
Answer : A - b
The reason why is you have refraction and reflection. Meaning, that you arrow B is being reflected.
I have included the vocabulary definitions I have studied for you and how I got the answer.
Refraction - It is the activity of bending the light. When the light that going from rarer medium to denser medium, the light soon bends towards its normal line.
Reflection - When the light ray is falling on the surface, then the ray that is coming from outside of the surface is known as a reflected ray.
In your reflection, the incident angle is now equal to the best reflected angle!
I hope this helps you!! ☺