Nucleic acid segment which is used to find the position of a gene and it forms a hybrid with this gene would be
Probe
The correct option is C.
Explanation for the correct option:
Option C:
Probes are DNA or RNA strands with specific nucleotide sequences complementary to VNTR (Variable Number Tandem Repeats) sequences that are used to find the position of a gene and form a hybrid with this gene.
Explanation for the incorrect options:
Option A:
Cloning is the process of generating a genetically identical copy of a cell or an entire organism.
Option B:
A vector, as related to molecular biology, is a DNA molecule (often plasmid or virus) that is used as a vehicle to carry a particular DNA segment or strand into a host cell as a part of a cloning or recombinant DNA technique.
Option D:
Retroviruses are viruses with RNA as genetic material.
Final answer: Nucleic acid segment which is used to find the position of a gene and it forms a hybrid with this gene would be Probe.