What is a nucleotide?
A.Carbon sugar
B.Nitrogen containing base
C.Phosphate
D.All of these

Hint:In the above question we have to choose what is the constituent of nucleotides. A nucleotide comprises a sugar molecule attached to a phosphate group and a nitrogen-containing base. The bases which are used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). In RNA, uracil (U) takes the place of thymine.

Complete answer:
We know that every generation inherits one thing or the other from their ancestors. The particles that are responsible for heredity are called chromosomes. They are made up of proteins and another type of biomolecule called nucleic acid. Nucleic acids are then sub categorised as DNA and RNA.
Let us now discuss the structure of these nucleic acids. These nucleic acids are made up of nucleoside and nucleotide.
Nucleoside consists of pentose sugar and nitrogenous base. It is the unit in which the base is attached to 1’ position of sugar. The number of nucleosides is done in a counter clockwise direction starting with 1’, then 2’ and so on.
Nucleotide is another building block of nucleic acid. When nucleoside is linked to phosphoric acid at a 5' position of sugar, then it is called nucleotide.
So, we can conclude that:
Nucleotide=nucleoside + phosphoric acid
As nucleoside consist of pentose sugar and nitrogenous base, we can write nucleotide as:
Nucleotide = pentose sugar + nitrogenous base + phosphoric acid.
Hence, we can say that nucleotides consist of carbon sugar, nitrogen containing base and phosphate.

Hence, option D is correct.

Note:
Nucleotides are organic molecules that serve as the monomer for the formation of nucleic acid polymers such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). These two components are the essential biomolecules within all life forms on earth.