In what way do two alleles for the same trait differ?

the answer to this predicament is false, by friend, i had this on a quiz, and i got it wrong, so i learned it, cos i was gonna have it on a test, and i got it right

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.