The blood of a person with the genotype AS for hemoglobin contains both normal (A) red blood cells and sickle shaped (S) blood cells, as shown in the picture below. What does this show?

A. Allele A is dominant over Allele S.

B. Neither Allele A or S is dominant and shows incomplete dominance.

C. Both allele A or S are dominant and shows co dominance.

D. Allele A and S are recessive traits.

The person is heterozygous (AS) for the sickle cell allele, so he has both the normal red blood cells as well as the sickle red blood cells.
Co-dominance is a pattern of Non-Mendelian inheritance in which neither alleles show a dominance over each other and both are expressed together in the same individual.
However, it is to be mentioned that if we consider the following conditions then the concept will be different:

Sickle Cell Anaemia: This disease can occur only in the individuals who have a homozygous sickle cell allele combination (SS), so for this disease the A (normal) allele is dominant over the S (sickle cell) allele as a homozygous (AA) or heterozygous(AS) combination of the normal allele prevents the disease.
Malaria Resistance: The malarial parasites can survive in normal red blood cells but not in sickle red blood cells. A person having the heterozygous (AS) allele combination is best suited to combat this disease as they have half sickle red blood cells. Also they are prevented from developing sickle cell anaemia due to the presence of half normal red blood cells. Here the sickle cell phenotype is dominant.