DNA molecule is directional. What does that mean?

a. Phosphate residue connects 5' carbons of the adjacent sugar residues
b. Phosphate residue connects 3' carbons of the adjacent sugar residues
c. Phosphate residue connects 5' and 3' carbons of the adjacent sugar residues
d. Nitrogenous base connects 5' and 3' carbons of the adjacent sugar residues
e. Phosphate residue connects 1' and 3' carbons of the adjacent sugar residues