Which is the best explanation of why DNA can be used to show relationships between species?

Question

a
DNA sequences will be similar among species that eat the same kinds of food.
b
DNA sequences will be similar in species that have evolved together through natural selection.
c
DNA sequences will be similar in species that undergo the same catastrophic events.
d
DNA sequences will be similar in species that are exposed to the same radiation sources.

Answer 1

b
DNA sequences will be similar in species that have evolved together through natural selection.