Research with Infants and Young Children Watching Videotaped Sequences of a Ball

Research with infants and young children watching videotaped sequences of a ball rolling off the edge of a ramp indicate that:

A) infants have an intuitive understanding of gravity and inertia.
B) 2-year-olds are sensitive to gravity, but not inertia.
C) 2-year-olds are sensitive to both gravity and inertia.
D) 6-year-olds are sensitive to both gravity and inertia but have not fully mastered these concepts.