Understanding Nucleotides and Nucleosides
Nucleotides and nucleosides are crucial components of nucleic acids, which play vital roles in cellular functions and genetic information storage.

Nucleotides
- Nucleotides are the building blocks of nucleic acids (DNA and RNA).
- Each nucleotide consists of three components:
- **Nitrogenous base**: This can be adenine (A), thymine (T), cytosine (C), guanine (G) in DNA, and uracil (U) in RNA.
- **Sugar**: In nucleotides, the sugar is either ribose (in RNA) or deoxyribose (in DNA).
- **Phosphate group**: This is attached to the sugar and is responsible for linking nucleotides together to form the backbone of nucleic acids.

Nucleosides
- Nucleosides are similar to nucleotides but lack the phosphate group.
- Each nucleoside comprises:
- **Nitrogenous base**: Identical to that in nucleotides.
- **Sugar**: Again, either ribose or deoxyribose.

Common Components
- The key components common to both nucleotides and nucleosides are:
- **Sugar**: Both contain a sugar molecule (ribose or deoxyribose).
- **Nitrogenous base**: Both include a nitrogenous base (A, T, C, G, or U).
Therefore, the correct answer to the question is option 'D' which states that both sugar and nitrogenous base are present in both nucleotides and nucleosides. The phosphate group, however, is only present in nucleotides and not in nucleosides. Understanding these components is essential for grasping the structure and function of nucleic acids in biology.