(A) is incorrect: Direct election of the lower house is a feature of Representative Democracy. Many Presidential systems (such as the USA) also have directly elected legislatures; therefore, this is not the distinguishing factor of a Parliamentary system. (B) is incorrect: The authority to amend the Constitution is a matter of Constitutional Sovereignty. This power exists in various forms of government, including both Parliamentary and Presidential models. (C) is incorrect: The fact that the Rajya Sabha is a permanent house is a Federal feature intended to maintain the representation of the States. It does not define the relationship between the Executive and the Legislature. (D) is correct: As per Article 75(3) of the Constitution, the Council of Ministers is collectively responsible to the Lok Sabha. This "Collective Responsibility" is the bedrock of the Parliamentary form of government, as the executive's survival depends on the support of the legislature.