An indication of the power of motor development is that babies on jolly jumpers learn to

A) Decrease the amplitudes of their jumps while increasing the variability of their jump periods
B) Decrease the amplitudes of their jumps while decreasing the variability of their jump periods
C) Increase the amplitudes of their jumps while increasing the variability of their jump periods
D) Increase the amplitudes of their jumps while decreasing the variability of their jump periods