Step 1: Identifying the psychological principle.
This situation illustrates cognitive dissonance, where individuals experience discomfort when their actions conflict with their prior attitudes.
Step 2: Role of incentive size.
When incentives are small, individuals lack sufficient external justification for their counter-attitudinal behaviour and therefore change their internal attitudes to reduce dissonance.
Step 3: Eliminating incorrect options.
Large incentives provide adequate external justification, leading to less attitude change. Hence, options (B), (C), and (D) are incorrect.
Step 4: Conclusion.
Thus, smaller incentives produce greater attitude change.
Final Answer: (A)