B.https://www.mansfieldct.org/Schools/MMS/staff/hand/genNaturalselection06.htm this is where I got my source.
10-35%25% based on the table the decrease of the table is 25%25%.Good Luck.
One way of creating a variation in a population is through genetic replication errors. This will make new type of alleles. Environmental factors causes variation such as affecting enzyme activity and function. The changes would show in the phenotype of an organism.