Answer:
C). When participants later completed the task alone.
Step-by-step explanation:
Muzafer's proposed his study of social conformity for which he selects the autokinetic effect and reveals that 'informational social influence'(as a stimulus) can help the participants estimate the portion of the movement of dot light as 'they were avoiding public embarrassment.'
As per the question, Sherif can counter this study when he discovered similar results 'when participants later completed the task alone' without any kind of informational social influence or ambiguous stimulus. This contradicts Sherif's study and hence, option C is the correct answer.