Option D is correct because federalism is defined as a system of government where governmental power is divided between different levels of government. The context clearly states that 'Federalism is a system of government in which the power is divided between a central authority and various constituent units of the country.' A key feature of federalism is that there are 'two or more levels (or tiers) of government,' and each tier has its own jurisdiction specified in the constitution. Both levels enjoy their power independent of the other.

Option A is incorrect because it describes a unitary system where sub-units are subordinate to the central government and receive powers from it. In a federal system, state governments have 'powers of its own for which it is not answerable to the central government.'

Option B refers to separation of powers among organs of government, not federalism.

Option C describes democracy, not the specific feature of federalism.