TOEFL Reading: ETS-TOEFL阅读机经 - 59OO0730VUEEPR55L$

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Social loafing does not occur when participants in the group believe that evaluating individual performance will improve the group's performance. B. The loafing effect is eliminated if the members of the group accept the standard by which their performance and that of the group is evaluated. C. Social loafing tends to disappear if the members of the group believe that their or the group's performance may be evaluated. D. Researchers have found that when group members receive monitoring and evaluation of their performance, their performance improves.