What is the most important non-genetic factor in preventing the onset of cognitive impairment?

Exercise

Explanation:

Cognitive impairment is the condition where a person has difficulty in recalling or remembering things. They also find it difficult to perform daily tasks and make decisions. They are not able to concentrate hence also have trouble learning new things. Cognitive impairment can be present genetically although it is observed almost in a large number of ageing people.

Exercise has been proven to help in cases of mild to severe cognitive impairment. In an experiment it was proven that 6 months of aerobic exercise reversed cognitive impairment symptoms in ageing people. It particularly benefits people carrying the APOE4 gene variant responsible for making people susceptible to Alzheimer's.  

equal distribution i think.

c should be the answer