Answer:
The correct answer is option B, that is, chlorophyll breaks down, exposing other pigment molecules we normally don't see.
Step-by-step explanation:
Leaves are colored because of the presence of the molecules known as pigments. Chlorophyll is the pigment, which makes the leaves to appear green. Chlorophyll is an essential element for plants as it helps the plant to synthesize food with the help of sunlight.
At the time of summer and spring, when there is enough amount of sunlight available, the plants produce loads of chlorophyll pigment. However, in autumn when it begins to get cooler, some of the plants stop producing chlorophyll, and those plants dissociate chlorophyll into smaller constituents. With the diminishing of chlorophyll, the other pigments begin to show their colors, and thus, the leaves turn red or yellow at the time of fall.