Which system is foundational according to the Basic Law of the Hong Kong Special Administrative Region?

The Basic Law of the Hong Kong Special Administrative Region establishes fundamental principles that underpin the governance and operational frameworks of the region. The choice emphasizing the social and economic systems, along with the mechanisms for protecting residents' fundamental rights and freedoms, as well as the three branches of government—executive, legislative, and judicial—captures the essential components that are pivotal for the functioning and stability of Hong Kong's governance under the principle of "one country, two systems."

This system forms the foundation upon which the SAR operates, ensuring that while it is part of China, it retains a high degree of autonomy in its social and economic affairs, and safeguards individual rights as specified under the Basic Law. The importance of these elements can be seen in their role in maintaining stability, promoting development, and protecting the rights of residents, which are key objectives outlined in the Basic Law.

The other choices introduce elements that, while relevant, do not serve as the foundational aspects specified by the Basic Law. For instance, foreign relations and defense policies are primarily under the purview of the central authority, and specific regulations such as health care or environmental laws are functional aspects rather than foundational systems of governance.