What does this structure mean in chemistry?

H O H
I II I
H - C - C - C - H
I I
H H

Clyde and marilyn are riding a roller coaster. during which section(s) of the track is their potential energy converted to kinetic energy? a. from point b to point c only b. from point b to point d only c. from point a to point b only d. from point a to point b and from point c to point d