Step 1: Background Understanding.
Fundamental Duties were not originally part of the Constitution when it came into force in 1950. They were added later to emphasize responsibilities of citizens along with their rights.
Step 2: Identifying the Amendment.
The 42nd Constitutional Amendment Act of 1976, also known as the "Mini Constitution," added Article 51A, which lists the Fundamental Duties. This amendment was introduced during the Emergency period under Prime Minister Indira Gandhi.
Step 3: Eliminating Wrong Options.
(B) The 44th Amendment restored democratic rights after the Emergency but did not add duties.
(C) The 73rd Amendment deals with Panchayati Raj institutions.
(D) The 74th Amendment deals with Municipalities.
Step 4: Conclusion.
Thus, the Fundamental Duties were added by the 42nd Constitutional Amendment Act.