The correct answer is option 'D' - The unicameral system of government.

Explanation:
The Kesavananda Bharati case, decided by the Supreme Court of India in 1973, is a landmark judgment that defined the basic structure doctrine of the Indian Constitution. The basic structure doctrine lays down the principle that certain features of the Constitution are beyond the amending power of the Parliament and cannot be altered or destroyed.

The basic structure features of the Indian Constitution, as identified by the Kesavananda Bharati case judgment, include:

a) Supremacy of the Constitution:
- The Constitution is the supreme law of the land, and all other laws and actions of the government must be in conformity with it.
- This ensures the protection of fundamental rights and the rule of law.

b) Unity and sovereignty of India:
- The Indian Constitution declares India to be a sovereign, socialist, secular, and democratic republic.
- It guarantees the unity and integrity of the nation and prohibits any act that undermines the sovereignty of India.

c) The democratic and republican form of government:
- The Constitution establishes a democratic system of government where the power is vested in the people.
- It provides for representative institutions, such as the Parliament and State Legislatures, where elected representatives make laws and govern the country.
- It also declares India to be a republic, where the head of state is elected and not a hereditary monarch.

d) The unicameral system of government:
- The unicameral system of government is not a basic structure feature identified by the Kesavananda Bharati case judgment.
- The Indian Constitution provides for a bicameral system of government at the federal level, with the Parliament consisting of two houses - the Lok Sabha (House of the People) and the Rajya Sabha (Council of States).
- The bicameral system ensures a system of checks and balances and allows for wider representation and deliberation.

In conclusion, the basic structure features of the Indian Constitution, as identified by the Kesavananda Bharati case judgment, do not include the unicameral system of government. The Indian Constitution provides for a bicameral system at the federal level.