Two randomly selected groups of 30 adults each were asked to write short stories on a particular topic. One group was told that the best stories would be awarded cash prizes, while the other group was not told of any prizes. Each story was evaluated by a team of judges who were given no indication of the group from which the story came. The stories submitted by those who thought they were competing for prizes were ranked on average significantly lower than the stories from the other group. Which one of the following, if true, most helps to explain the difference in average ranking between the two groups' stories? ['People writing to win prizes show a greater than usual tendency to produce stereotypical stories that show little creativity.', 'The cash prizes were too small to motivate an average adult to make a significant effort to produce stories of high quality.', 'Most adults show little originality in writing stories on a topic suggested by someone else.', 'No one explained clearly to either group what standards would be used in judging their stories.']