Answer:
populations
Explanation:
A) genotypes
Natural selection may happen because of different genotypes (for example, heterozygous individuals survive better). Natural selection does not change genotype.
Recall that genotype is the type of alleles one has.
B) populations
Natural selection is the survival of the fittest. For example, a drought. Or predators. Or limited food supply. Or overproduction. All will end up with the stronger, better-surviving types of a certain population. Natural selection does change populations.
C) individuals
Natural selection usually occurs when there are large amounts of a certain type of individual (for example, bunnies). They usually do not affect individuals.
D) phenotypes
Natural selection may happen because of different phenotypes (for example, green grasshoppers survive better than red ones). Natural selection does not change phenotype.
Recall that phenotype is the physical appearance one has.
Extra:
Phenotype vs. Genotype:
If A is dominant for brown hair and a is recessive for albino hair:
Genotype Aa has a phenotype of brown hair.
Genotype AA has the phenotype of brown hair.
Genotype aa has the phenotype of albino hair.
You can see how genotype and phenotype are like.
