Which of the following conditions represents the codominance of genes?

• A
  The gene suppresses the traits of its alleles and expresses its own traits.
• B
  When genes are separate,they have the same phenotype,but when they interact together,they produce a new phenotype.
• C
  When both types combine to produce traits,they resemble one of the two parents.
• D
  During the heterozygous state,both alleles express their traits independently.