Correct Answer: (d) Golden Quadrilateral
Note: The national highway network connecting Delhi, Mumbai, Chennai and Kolkata is called Golden Quadrilateral. The Golden Quadrilateral is a national highway network connecting most of India's major industrial, agricultural and cultural centres.
The Diamond Quadrilateral is a project of the Indian Railways to establish a high-speed rail net- work in India. The Diamond Quadrilateral will connect the four mega cities of India, viz. Del- hi, Mumbai, Kolkata and Chennai, similar to the Golden Quadrilateral highway system.