Explanation:

The correct answer is option 'A', Keshavananda Bharati Case, 1973.

Keshavananda Bharati Case, 1973:
The Keshavananda Bharati Case is a landmark judgment of the Supreme Court of India that established the basic structure doctrine of the Constitution. In this case, the Supreme Court ruled that the Preamble indicates the basic structure of the Constitution.

Basic Structure Doctrine:
The basic structure doctrine holds that there are certain principles and provisions of the Constitution that are sacrosanct and cannot be amended by the Parliament. These principles and provisions form the basic structure of the Constitution and act as a check on the power of the Parliament to amend the Constitution.

Key Points:
- The Keshavananda Bharati Case was heard by a 13-judge bench of the Supreme Court.
- The case arose from a challenge to the Kerala government's attempt to acquire the properties of the Keshavananda Bharati, the head of a Hindu matha (monastic organization).
- The petitioner argued that the government's actions violated their fundamental right to property.
- However, during the course of the case, the issue of the limits of the amending power of the Parliament was also raised.
- The Supreme Court, in its judgment, held that while the Parliament has the power to amend the Constitution, this power is not absolute and can be limited by the basic structure of the Constitution.
- The Court further held that the Preamble of the Constitution, which sets out the objectives and values of the Constitution, indicates the basic structure of the Constitution.
- The Court did not provide an exhaustive list of what constitutes the basic structure but held that certain fundamental rights, the principle of federalism, secularism, and democracy are part of the basic structure.
- The judgment in the Keshavananda Bharati Case has been regarded as one of the most important judgments in the history of the Indian judiciary as it established the basic structure doctrine and limited the power of the Parliament to amend the Constitution.