Explanation:

- Single Citizenship and Parliamentary System of Government:

- These features are adopted from the UK.

- Single Citizenship implies that all Indians are citizens of India, similar to the UK where there is no separate citizenship for different countries within the UK.

- The parliamentary system in India is modeled on the British system.

- The UK emphasizes the prime ministerial form of government, party system, and the rule of law.

- Option:1, Australia:

- Influenced Indian constitutional elements such as concurrent powers and the terminology within the Constitution.

- Option:2, Canada:

- Contributed ideas like a federal system with a strong central government.

- Option:3, The US:

- Contributed the concept of a written constitution, judicial review, and the idea of a Supreme Court.

- Option:4, The UK is correct.