À is a segment of DNA which codesfor a specific trait

A gene is a segment of DNA which codes for a specific trait.

Explanation:

Cellular development, replication, and cell repair are controlled by genetic information stored within DNA molecules. The long-chain, helical macromolecules of these deoxyribonucleic acids, are constructed from complex sequences of covalently bonded monomers called nucleotides.  

Genes, can span several nucleotides and even multiple chromosomes. They are encoded through the processes of transcription, translation to become proteins, that determine physical characteristics or phenotypes.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.