The nucleic acid of bacteriophages enters the host cell naked, leaving the capsid outside the cell. Plant and animal viruses can enter through endocytosis, in which the cell membrane surrounds and engulfs the entire virus.

The correct answer is option 'C' - Nucleic acid.

Explanation:
A virus is a microscopic infectious agent that requires a host cell to replicate. It is composed of a few key components: an outer envelope (in some viruses), a capsid, and nucleic acid.

1. Envelope:
- Some viruses have an outer envelope made up of lipids and proteins.
- This envelope helps the virus to attach to and enter the host cell.
- It also provides protection to the virus and helps it evade the host's immune system.
- However, not all viruses have an envelope.

2. Capsid:
- The capsid is the protein coat that surrounds the nucleic acid of the virus.
- It provides protection to the viral genome (nucleic acid) inside.
- The capsid is composed of repeating protein subunits called capsomeres.
- It gives the virus its characteristic shape, whether it is helical, icosahedral, or complex.

3. Nucleic acid:
- The nucleic acid is the genetic material of the virus, which can be either DNA or RNA.
- It contains the instructions for the virus to replicate and produce new viral particles.
- When a virus infects a host cell, it introduces its nucleic acid into the host cell.
- The viral nucleic acid takes over the cellular machinery of the host cell and uses it to replicate and produce more viral particles.
- The viral nucleic acid is responsible for the synthesis of viral proteins and the assembly of new viral particles.
- This process eventually leads to the release of new viral particles, which can then infect other host cells.

In summary, while both the envelope and capsid are important components of a virus, it is the nucleic acid that enters into the host cell. The nucleic acid carries the genetic information of the virus and directs the replication process within the host cell.

Nucleic acid alone enters into the host. All other parts will be left behind and will not enter the host. So answer is option c.