DNA is double stranded, and the strands are antiparallel because they run in opposite directions. Each DNA molecule has two strands of nucleotides. Each strand has a sugar-phosphate backbone, but the orientation of the sugar molecule is opposite in the two strands. Thus the main reason of this antiparallel nature of the DNA is the presence of a phosphodiester bond that links the phosphate group to the hydroxyl group of the sugar molecule (present in alternate directions on either strand).
So, the correct option is 'phosphodiester bonds'.
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