The center of the DNA molecule, the rungs of the ladder, are composed of

A. phosphates only.

B. nitrogenous bases only.

C. phosphates and sugars.

D. nitrogenous bases and sugars.

B. Nitrogenous bases only

Sugar and phosphates form the backbone of DNA molecule. On the other hand, the rungs of the ladder or the connecting region of both strands is composed primarily of nitrogenous bases. The nitrogenous bases pair with each other in a complementary fashion to form the rung. Adenine and thymine pair with each other whereas cytosine and guanine pair with each other.