Hydrangea Plants of the Same Genotype Are Planted in a Large

Hydrangea plants of the same genotype are planted in a large flower garden. Some of the plants produce blue flowers and others pink flowers. This can be best explained by which of the following?

A) Environmental factors such as soil pH
B) The allele for blue hydrangea being completely dominant
C) The alleles being codominant
D) The fact that a mutation has occurred
E) Acknowledging that multiple alleles are involved