樓上的英語?
In two teams of athletes,we supply one team (Team A) with energy bar for diet but not for another team (Team B).It is to find out whether the standard of jogging these teams of athletes can be improved?
If one of the athletes from Team A is a friend of the Team B,then the Team B will know that Team A has energy bar daily,but not for their team.In this case,Team B will work harder everyday in order not to loose out.Eventually,both teams will improve their speed in jogging etc..This experiment hence can't distinguish whether the energy bar has to do with the improvement of the speed.