题目选项分析

Of the 60 participants in a clinical trial, 30 participants were considered to be in the experimental group, and were administered a large dose of an experimental painkiller called nexaphedrinol, while the 30 remaining participants were considered to be in the control group, and were administered the same dose of a placebo. Afterward, participants in the experimental group exhibited fine motor skills that were more diminished than those of the control group. The observed detrimental effects on fine motor skills were attributed to a compound in nexaphedrinol called phedrine, which temporarily damages nerve endings.

Which of the following, if true, would best support the conclusion that a certain compound in the painkiller was responsible for the observed results?

【选项】All the participants in the experiment were found to have had comparable fine motor skills prior to the administration of the nexaphedrinol or the placebo.