Final answer:
Chromosomes are primarily made of DNA, which carries genetic information for the development and functioning of organisms.
Step-by-step explanation:
Chromosomes are coiled structures made of DNA and proteins. They are located within the cell nucleus and are composed primarily of DNA, which encodes the genetic instructions necessary for the development and functioning of living organisms.
These instructions are organized into units called genes, and most genes contain the information needed to make a single protein, although some genes code for RNA products.
Chromatin is the combination of DNA and proteins that make up the chromosomes. In eukaryotic cells, chromatin exists in a less condensed form when the cell is not undergoing division. When the cell prepares to divide, the chromatin condenses to form distinct chromosomes.
Each species has a particular number of chromosomes; humans have 46, for example. Proteins such as histones help package the DNA in chromatin, playing a role in the regulation of gene expression.
To answer the student's question directly: Chromosomes are primarily composed of option d) DNA.