The relationship between intron and exon

A exon is a portion of your dna that is expressed as a gene

the introns are just space in between the exons that are cut out during transcription

A large portion of your DNA is a bunch of nothing which is believed to have been caused by retroviruses that inserts its DNA into yours. These introns serve as a huge benefit to us as they are what keeps our genes from getting all screwed up from all the random mutations that happen in our DNA. Since more than 95% (Most likely more don't really remember) is introns a mutation happening on any part of your dna is most likely to happen on the intron which is not expressed. The exons are the expressed dna which are your genes. These are the parts that are used to manufacture the proteins in your body

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.