Answer: The correct answer is- A. Chromosome numbers vary widely.
Chromosome can be described as thread like structure that is composed of DNA ( deoxyribonucleic acid) and possesses genes ( segment of DNA coding for a particular protein) on it.
Eukaryotic cells ( such as plant cell, animal cell) have variable number of chromosomes.
For instance, human beings have 23 pairs of chromosomes whereas it is different in plants depending on the species.
Thus, A) is the right answer.