A mother and her baby are at the park, and the baby is swinging on a swing. At one point, the mother brings the swing up to her face, momentarily holds it at rest, then pushes the swing. The baby swings away from the mother, and then swings back. If the mother does not move, is she in danger of being struck by the swing? 

a. No, because conservation of energy indicates that the swing can only return to its original height.

b. Yes or no, depending on the amount of frictional forces acting on the baby and swing. 

c. Yes or no, depending on the combined mass of the baby and swing. 

d. Yes, because the swing had both gravitational potential energy and kinetic energy when it was released, it could rise to a higher height and strike the mother's face.