Concept: The Competition Act, 2002 was enacted to prevent practices having adverse effect on competition, promote competition, protect consumer interests and ensure freedom of trade.
Step 1: Understand the purpose of the Act.
The Act replaced the older MRTP framework and created a modern competition law regime in India.
\[
\text{Competition Act} \Rightarrow \text{Fair competition + Consumer welfare}
\]
Step 2: Identify the commencement date.
The Competition Act, 2002 came into force on:
\[
31^{st}\ March,\ 2003
\]
Step 3: Select the correct option.
Among the given options, 31st March 2003 is option (D).
Therefore, the correct answer is 31st March 2003.