Birds learn to fly by _____ . A: preys B: instinct C: referees

The experiment conducted by the researcher was meant to______. A: review the decisions of referees at the 1998 World Cup B: analyse the causes of errors made by football referees C: set a standard for football refereeing D: reexamine the rules for football refereeing

According to the third paragraph, improper calls on the football field ______. A: are evidence of corruption by some officials B: are increased by the higher speed of the game C: result from reduced proficiency of referees D: are caused by anything other than human error