B
eliminate one choice each
we start with A
no immagration occured in the process
the question didn't tell you that they were originated from another place or something like that
the second choice B
well, the people that survived are from one allele so i think it is the choice
the third choice
it didn't say the population was small in number,but the purple all individuals are dying.However, the population may inctease due to the abnormal fertility of red allele individuals
the fourth choice
well, no mutation occur he didn't mention?change in Alleles or one individual with strange genetic features has suddenly appeared