The rung or steps of dna are made up of

In between the two sides of this sugar-phosphate backbone are four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). (A grouping like this of a phosphate, a sugar, and a base makes up a subunit of DNA called a nucleotide.)

option a and d is the correct answer

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plz mark as the brainliest answer

the answer is "a.) well–developed vascular system."

explanation: