Concept:The centromere is the region where the two identical strands of a chromosome are held together.
Explanation:A chromosome consists of two identical strands known as sister chromatids.
These sister chromatids are joined at a special region called the centromere.
During cell division, the centromere also serves as the attachment point for spindle fibres.
The spindle is involved in separating chromatids, not joining them.
Cellulose is a structural material found in plant cell walls.
A chromatid is one of the two strands themselves, not the joining structure.
Thus, the structure that joins the two strands of a chromosome is the centromere.
Answer: C. centromere