A strand of DNA or RNA consists of nucleotides linked together by phosphodiester bonds. A phosphodiester bond exists between the phosphate of one nucleotide and the sugar 3' carbon of the next nucleotide. This forms a backbone of alternating sugar and phosphate molecules known as the sugar-phosphate backbone.The two strands of DNA are also antiparallel (run in opposite directions) to one another. A strand of DNA can have direction 5'-3' or 3'- 5'.One strand of the DNA molecule is 5'-3' and the other strand is 3'-5'. A DNA strand is assigned direction based on what is found at the end of the strands. The end of the strand with a free phosphate is the 5' end because phosphate attaches to the 5' carbon of the sugar. The end with a free OH group is the 3' end because the OH group is attached to the 3' carbon of the sugar.So, the correct answer is option D.