Gene S Controls the Sharpness of Spines in a Type

Multiple Choice

Gene S controls the sharpness of spines in a type of cactus.Cactuses with the dominant allele,S,have sharp spines,whereas homozygous recessive ss cactuses have dull spines.At the same time,a second gene,N,determines whether or not cactuses have spines.Homozygous recessive nn cactuses have no spines at all.The relationship between genes S and N is an example of

A) incomplete dominance.
B) epistasis.
C) complete dominance.
D) pleiotropy.