Answer: The correct answer is- A) chromosome.
Chromosome can be described as thread like structure that is composed of nucleic acid DNA ( deoxyribonucleic acid), which is tightly wound around histone protein many times that support its overall structure.
They are found in the cells of living organisms as very long strands.
The nucleic acid DNA is made of small units called nucleotides ( that contain nitrogenous base, phosphate, and deoxyribose sugar).
Genes ( segment of DNA that correspond to particular protein) are located on chromosomes and they are inherited by offspring from their parents.
Allele is the variant of a gene ( alternative form of a gene).
Thus, option A) is the right answer.