The biochemical analysis of different chlorophyll pigments in plants would be most useful in
a. how plants reduce asexually
b. how plants pass favorable traits to their offspring
c. why some plants produce hemoglobin
d. which plants might have a common ancestor

The biochemical analysis of different chlorophyll pigments in plants would be most useful in determining D. which plants might have a common ancestor.
The field of biology that deals with the similarities between these plants is called comparative biochemistry. If these plants have similar DNAs, then they are more closely linked in evolutionary terms, and thus it is quite possible they have the same predecessor.