Re tilting, how does that work? Pretty certain the path is not in a plane.
If you pass a plane at an angle through a cylinder and unwrap the cylinder you get a sinusoidal curve, not a parabola.
I also had argued for A in question 20, and saw that Matrix Education put D.
Prior to that, attempting to verify with a different method, I had tried to solve it using the Lagrangian method (I used sections 6.1 and 6.3 of
David Morin's book) and it seems to confirm A...