A study of 8, 000 randomly chosen adults in a European country found that 75 percent of those who consumed alcohol an average of twice or more per week over a six-month period suffered at least one cold during that period. We can tentatively conclude from this that consuming alcohol tends to increase one' s susceptibility to colds. Which one of the following, if true, would most weaken the argument? ['Sixty percent of those in the study who did not suffer any colds over the six-month period consumed alcohol once per week or more.', 'Seventy-five percent of those in the study who never consumed alcohol suffered at least one cold over the six-month period.', 'Fifty percent of those in the study who consumed alcohol an average of once per week suffered colds over the six-month period.', 'Eighty percent of those in the study who consumed alcohol three times or more per week suffered colds over the six-month period.']