Apolygenic trait can have

a. fewer genotype than most single-gene traits.

b. many possible genotypes, but few possible phenotypes

c. fewer phenotypes than most single-gene traits.

d. many possible genotypes, producing many possible phenotypes.

I believe the correct response would be D. A polygenic trait encodes for something as melanin concentration in one's skin, skin colour, height etc. These vary quite immensely from person to person, for instance, and can not only be stated as discrete categories in terms of phenotype, as short and or tall. Since the many phenotypes are based on the appropriate Genotypes, there must be many possible Genotypes as well to code and or provide for these diverse phenotypes within a given polygenic trait.