Which of the following statements about dna are true?

(a) the bases are located inside the helix formed from two polynucleotide strands.
(b) the grooves all have the same dimensions.
(c) the two strands run in the same direction.
(d) within experimental error, the mole percent adenine was always the same as the mole percent thymine, while the mole percent guanine was always the same as that of cytosine.