There is a Parliamentary System of Government in India because the

The correct option is Council of Ministers is responsible to the Lok Sabha.

In a Parliamentary System of Government, the executive is branch of government is responsible to the legislature for its policies and actions. In India, this principle is constitutionally enshrined in Article 75(3), which explicitly states that the Council of Ministers shall be collectively responsible to the Lok Sabha (the House of the People).
This collective responsibility means that the government remains in power only as long as it enjoys the confidence of the majority of the members in the Lok Sabha. If the Lok Sabha passes a no-confidence motion, the entire Council of Ministers must resign.

Let's examine why the other options do not define a parliamentary system specifically:
1. Lok Sabha is elected directly by the people: This is a feature of a democratic system, but not exclusively of a parliamentary one. For instance, in a Presidential system like in the United States, the House of Representatives is also elected directly by the people.
2. Parliament can amend the constitution: The power to amend the constitution exists in both parliamentary and presidential systems (e.g., the US Congress can propose amendments). It is a feature of constitutional supremacy or amendment procedure, not a defining characteristic of a parliamentary system.
3. Rajya Sabha cannot be dissolved: This represents the permanent nature of the upper house of parliament, ensuring continuity in the legislative process. It does not establish the relationship between the executive and the legislature, which is the hallmark of a parliamentary system.

Therefore, the collective responsibility of the Council of Ministers to the lower house of the legislature (Lok Sabha) is the essential feature that defines India's Parliamentary System of Government.