In dna double helix, the two dna chains are held together by a) covalent bonds between the pair of bases b) hydrogen bonds between the pair of bases c) ionic bonds between the pair of bases d) none of the above

the answer is b.) hydrogen bonds between bases.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.

i think the answer is c hope this