Two motorboats are traveling down a river. Motorboat 1 has a mass of 6,000 kg, and motorboat 2 has a mass of 1,500 kg. The graph below shows the kinetic energies of the boats as they gain speed.

If both boats gain speed at the same rate, why does motorboat 1 have more kinetic energy?
A.
It has more mass.
B.
It encounters more air resistance.
C.
Its length is greater.
D.
It sits up higher in the water.