Answer: The correct answer is- A) gene > DNA > chromosome > nucleus.
A gene can be described as segment of DNA ( deoxyribonucleic acid) that codes for specific protein, which inturn determines the trait/ characteristic of an individual.
Chromosomes are the threadlike structures that are composed of DNA and they are present within the nucleus of eukaryotic cells ( suh as plant and animal cell).
Thus, flow chart in option A) correctly shows the relationship between the cell structures that are listed.