Test analysis: This is an optimal multiple-choice question, because Hong Kong and Macao have special historical reasons and realistic situations, and they practice the capitalist system. Based on this, they have differences in autonomy, economic policy and diplomatic rights. And the difference of social system is their most typical difference. The answer is a.

Comments: This question is difficult, mainly to examine students' knowledge and understanding of ethnic areas and the depth and breadth of autonomy in Hong Kong and Macao.