Answer:C) the nitrogenous bases
D) AGCT represent nitrogenous bases: Adenine, Guanine, Cytosine and Thymine respectively.
E) The structure of DNA is supported by a backbone called deoxyribose sugar
F) The complementary strand is TACGTC
Explanation: A nucleotide is consist of a nitrogenous base, a deoxyribose sugar and a phosphate group. The nitrogenous bases found in DNA are Adenine, Guanine, Cytosine and Thymine and are represented as A, G, C, and T respectively. The bases in one DNA strand from bonds with the bases in the complementary strand thus forming steps in the double stranded DNA. In bond formation among the bases, Adenine bonds with Thymine while Guanine bonds with Cytosine. Therefore in a double stranded DNA, wherever G is found in one strand, C occurs in the complementary strand and wherever A is found, T occurs in the complementary strand.