If the base pairs in a dna strand were held together with covalent bonds instead of hydrogen bonds, how would cells have to operate differently? a) new dna would need to be made each time the strand was opened. b) the cell would have to take in and use more energy in order to break the covalent bonds. c) each time the dna strand opened the cell would need to replace the nitrogenous bases. d) the cell could only open and close the dna strand when it replicated.