Which is the longest National Highway in India?

Explanation:

National Highways connect the country's most remote areas. The Central Public Works Department constructs and maintains these important road systems (CPWD). A number of large national highways operate in both directions, north-south and east-west. Between Delhi and Amritsar, the historic Sher-Shah Suri Marg is known as National Highway No. 1. NH-44, which runs from Kanyakumari in Tamil Nadu to Srinagar in Jammu and Kashmir, is now India's longest highway. An old numbering system designated a part of this route as NH 7, with its northern terminus in Varanasi, Uttar Pradesh.

Final Answer:  Hence, the correct answer is option (D) i.e.NH - 7.