The answer is C.
I'm thoroughly confused! The question is asking for when the magnitude of the vertical component of the force that the wall exerts on the left end of the beam is the smallest. How can a wall that is perpendicular to the beam exert a force in any direction other than directly to the right? When would there ever be a vertical component?
Am I missing some sort of fundamental understanding about how forces work? If I exert a force on a wall by pushing it with my hand and forearm at an angle, by Newton's third law, is the wall capable of exerting a force on my arm at the same angle? Or is it only going to exert a force equal to the horizontal component of my force?