Introduction:
A cloning vector is a DNA molecule used to carry foreign DNA fragments and replicate them inside a host organism. It is an essential tool in genetic engineering and molecular biology. Cloning vectors possess several desirable features that allow for efficient cloning and manipulation of DNA fragments. However, there are certain features that are not desirable in a cloning vector.

Explanation:
Among the given options, the feature that is not desirable in a cloning vector is the presence of two or more recognition sites (Option C). Here's why:

Presence of a marker gene:
- A desirable feature of a cloning vector is the presence of a marker gene that allows for easy identification and selection of transformed cells.
- Marker genes can confer resistance to antibiotics (e.g., ampicillin) or enable the production of a visual marker (e.g., green fluorescent protein).
- The presence of a marker gene helps in distinguishing between transformed and non-transformed cells, ensuring successful cloning.

Presence of a single restriction enzyme site:
- A desirable feature of a cloning vector is the presence of a single restriction enzyme site.
- Restriction enzymes are used to cut DNA at specific recognition sites, allowing for the insertion of foreign DNA fragments into the vector.
- A single restriction enzyme site ensures that the insert DNA is correctly oriented and prevents self-ligation of the vector.

Presence of origin of replication:
- Another desirable feature of a cloning vector is the presence of an origin of replication.
- The origin of replication is a DNA sequence that allows for the replication of the vector in the host organism.
- This ensures that the vector and the inserted DNA fragments are replicated and maintained during cell division.

Presence of two or more recognition sites:
- The presence of two or more recognition sites in a cloning vector is not desirable because it can lead to multiple insertions of DNA fragments.
- Multiple insertions can result in rearrangements, deletions, or insertions of DNA fragments at unintended locations.
- This can complicate the analysis and manipulation of the cloned DNA fragments.

Conclusion:
In summary, the presence of two or more recognition sites is not a desirable feature of a cloning vector. It can lead to multiple insertions of DNA fragments and complicate the analysis and manipulation of the cloned DNA.