Answer: B. the 5'-3' orientation of the polynucleotide strand .
The complimentary pairing of DNA molecules ensures 5' 3' and 3'[ 5 ' arrangement for correct pairing of purines and pyrimidine (Adenine E with thymine and cytosine with guanine) in opposite direction. .
RNA only contains five prime and three prime only, but DNA contains both 5'3' and 3'5'.
