A gazelle is born with slightly longer legs which allow it to run faster than the other gazelles in the herd. This adaptation came may have come about because
a. the gazelle needed to be able to run faster.
b. the gazelle's parents were not able to outrun a cheetah.
c. there was a mutation in the gazelle's genetic code.
d. the gazelle did not get enough nutritious food after it was born.