An example of codominance is:
A. Black and brown spotted coat color in horses.
In codominance, both alleles in a heterozygous organism contribute to the phenotype, resulting in a phenotype that shows both traits simultaneously, as seen in the spotted coat of horses. The other options represent different types of inheritance: B (seed shape) refers to complete dominance, C (Labrador coat color) has a different inheritance pattern, and D (plant heights) also shows complete dominance.