Answer:
3.
Explanation:
There are four nitrogenous bases in a DNA including guanine (G), adenine (A), cytosine (C) and Thymine (T) and together they form the nitrogenous base sequence arranged in a specific order of three letters such as GAC and TAG to form a genetic code.
These nitrogenous base sequences forming genetic code are amino acid specific and determine the amino acid sequence in DNA. for example: CTT determines leucine and GTT determines valine.
Hence, the correct option is "3".