Two objects have the same size and shape but one of them is twice as heavy as the other. They are dropped simultaneously from a tower. If air resistance is negligible, 

a. The heavy object strikes the ground before the light one
b. They strike the ground at the same time, but the heavy object has the higher speed
c. They strike the ground at the same time and have the same speed
d. They strike the ground at the same time, but the heavy object has the lower acceleration because it has more mass