What do diffraction and refraction have in common? pick only one

they both involve interference.
they both involve wave interactions.
they both involve reflection.
they both involve construction.

Answer;

They both involve wave interactions

Explanation;Refraction is a property of a wave that refers to the bending of a wave as it moves from one medium to another.Diffraction on the other hand is a property of a wave such that an object causes a wave to change direction and bend towards it.Diffraction and refraction differ in that, refraction occurs when waves pass through an object while diffraction occurs when waves pass around an object.The similarity between refraction and diffraction is that they both involve interactions of waves and causes waves to bend thus changing their direction.

This is the answer of your question