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.
The statement "Seventy-five percent of those in the study who never consumed alcohol suffered at least one cold over the six-month period" would most weaken the argument.