Please Use the Following Information to Answer the Question(s) Below

Please use the following information to answer the question(s) below.
A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negative and is designated by the alleles R and r, respectively. A third gene for the MN blood group has codominant alleles M and N.
-If an organism is diploid and a certain gene found in the organism has 18 known alleles (variants) , then any given organism of that species can/must have which of the following?

A) at most, 2 alleles for that gene
B) up to 18 chromosomes with that gene
C) up to 18 genes for that trait
D) up to, but not more than, 18 different traits