Answer: A. environmental influences
A development in terms of biology is a gradual process of changes that occurs in an organism until the organism attains maturity or adulthood. Development can be physiological and mental development. Environmental influences are influences of nature on development. Some of the environmental influences are nutrition, altitude, temperature and climate. For example sunny weather conditions in a region can induce dark complexion in the habitants.
Incomplete dominance produces a new heterozygous phenotype such as the purple color in this example