Critical Reasoning (CR) | An international study recently examined the effects of second-hand

An international study recently examined the effects of second-hand smoke on health. Surprisingly, although the dosages of harmful chemicals from second-hand smoke are so small that their effect should be negligible, the study found that nonsmoking spouses of smokers displayed an incidence of heart disease that was significantly greater than that of nonsmokers who were not as regularly exposed to second-hand smoke.

Each of the following, if true, could contribute to an explanation of the unexpectedly
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