A headline atMSNBC.comstated:"One way to ward off Alzheimer's:Take ahike.Study:Walkingat least one mile a day reduces risk of cognitive impairment by half."The article reports on a study showing that elderly people who walked a lot tended to have more brain mass after9years and were less likely to develop dementia that can lead to Alzheimer's disease than subjects who walked less.At the start of the study the researchers measured the walking habits of the elderly subjects and then followed up with measures of brain volume nine years later.The active walkers had more brain mass and fewer dementia symptoms.

Is it valid to conclude that walking at least one mile a day will reduce risk of cognitive impairment,asthe headline states?

a.Yes, the study provedthat walking daily caused an increase in brain mass and reduced dementia symptoms.

b.Yes since the study measured 2quantitative variables:walking and cognitive dementia.

c.No, the study was an experiment but randomization was not done.

d.No, the study was an observational study so "cause and effect" cannot be proven.