Double-stranded DNA looks a little like a ladder that has been twisted into a helix, or spiral. The side supports of the ladder are

a. individual nitrogenous bases.

b. alternating bases and sugars.

c. alternating bases and phosphate groups.

d. alternating sugars and phosphates.

e. alternating bases, sugars, and phosphates.

d) alternating sugars and phosphates.

Explanation:

DNA is a molecule which acts as the genetic material of the organisms on Earth. The DNA is made of the monomer units called nucleotides which are composed of a sugar called deoxyribose, a phosphate group and two types of nitrogenous bases (purines and pyrimidines).

The DNA structure is known as the double-helical model which gives a ladder-like appearance in a twisted manner. The backbone of the ladder or DNA is made of the deoxyribose sugar and the phosphate group whereas the nitrogenous bases are arranged inside the DNA.

Thus, option-D is the correct answer.