You accidently bump into a bokcase. It tils briefly but then returns to upright, and you breathe a sigh of relief. When you first bumped the brookcase, its center of gravity moved.
A. Upward and its gravitational potential energy increased.
B. downward and its gravitational potential energy decreased.
C. downward and its gravitational potential energy increased.
D. upward and its gravitational potential energy increased.
