Step 1: Identify what changed in the Preamble.
The 42nd Constitutional Amendment Act, 1976 inserted three words into the Preamble: “Socialist,” “Secular,” and “Integrity” (modifying “unity of the nation” to “unity and integrity of the Nation”).
Step 2: Why the 42nd, not others?
24th (1971) empowered Parliament regarding amendment and made presidential assent mandatory; 44th (1978) rolled back several Emergency-era changes but did not alter Preamble wording; 73rd (1992) concerns Panchayats—no Preamble edit.
Step 3: Conclude.
\[
\boxed{\text{Preamble was amended by the 42nd Amendment (Option B).}}
\]