Step 1: Understanding industrial belts.
Industrial belts are clusters of industries located in specific regions of India, formed due to the availability of raw materials, power supply, transport, skilled labor, and favorable market conditions. These belts play a crucial role in India's industrial geography.
Step 2: Checking each option.
- Bengaluru - Coimbatore - Madurai: Known for textiles, information technology, and machine tools. This is a well-recognized industrial belt in southern India.
- Mumbai - Pune: One of the oldest and most significant industrial regions in India, known for automobiles, engineering, petrochemicals, and IT.
- Ahmedabad - Vadodara: Famous for textiles, chemicals, pharmaceuticals, and engineering industries. This is a strong industrial corridor in Gujarat.
- Hugli Region (West Bengal): An important historical industrial belt, known for jute, engineering, chemicals, and other manufacturing industries.
Step 3: Conclusion.
All four listed regions (i, ii, iii, iv) are recognized industrial belts in India. Hence, the correct answer is option (D).
\[
\boxed{\text{All four regions (i, ii, iii, iv) are well-known industrial belts in India.}}
\]