The correct answer is option 'A', the Regulating Act of 1773.

The Regulating Act of 1773 was an important act passed by the British Parliament to regulate the affairs of the British East India Company in India. It was the first major step taken by the British government to establish control over the Company's administration and to introduce reforms in its functioning.

The act had several provisions, one of which was the establishment of a Supreme Court at Calcutta. This provision was significant as it marked the beginning of the separation of powers between the executive and the judiciary in British India.

Below are the key points related to the establishment of the Supreme Court at Calcutta under the Regulating Act of 1773:

1. Background: Prior to the establishment of the Supreme Court, the British East India Company had its own courts to administer justice in its territories. However, these courts were often accused of corruption and favoritism, leading to a lack of faith in the British legal system.

2. Objectives: The primary objective of establishing the Supreme Court was to ensure impartial and independent administration of justice. It aimed to bring British law and legal procedures to India and provide a fair and transparent judicial system.

3. Composition: The Supreme Court was to consist of a Chief Justice and three other judges, all appointed by the Crown. The Chief Justice and one of the other judges were required to be barristers or advocates of at least five years' standing in England.

4. Jurisdiction: The Supreme Court had jurisdiction over British subjects in Bengal, Bihar, and Orissa. It had the power to hear and decide civil and criminal cases, including those involving British officials, merchants, and the Indian population.

5. Appeal: The Supreme Court's decisions could be appealed to the Privy Council in England, which was the highest court of appeal.

6. Impact: The establishment of the Supreme Court brought about significant changes in the legal system of British India. It introduced the principles of British common law, equity, and statutes into the Indian legal system. It also paved the way for the establishment of similar courts in Madras and Bombay in the later years.

In conclusion, the Regulating Act of 1773 provided for the establishment of the Supreme Court at Calcutta. This provision was a significant step towards introducing an independent judiciary in British India and bringing about reforms in the administration of justice.