The correct answer is C) shock loading on the tow line is reduced. When the tug and tow ride the wave crests simultaneously, it helps to reduce the shock loading on the tow line. This is because the tug and tow move up and down together, minimizing the sudden jerking motions that can occur when they are out of phase with the waves. Reducing shock loading helps prevent damage to the tow line and other towing equipment. The other options are incorrect. Option A is incorrect because the visibility of the tow from the tug is not the primary reason for synchronizing the motion. Option B is incorrect because the catenary (curve) of the tow line is not directly affected by the tug and tow riding the wave crests together. Option D is incorrect because towing speed is not the main factor, but rather the reduction of shock loading on the tow line.