The correct answer is: A. NH-28
NH-28 is the longest national highway in Bihar. It is a 1,395-km-long highway that runs from Varanasi in Uttar Pradesh to Moreh in Manipur. The highway passes through the states of Bihar, Jharkhand, West Bengal, Assam, and Manipur.
NH-28 is a two-lane highway that is being upgraded to a four-lane highway. The highway is an important link between the eastern and northeastern states of India. It is also an important trade route between India and Myanmar.
The other options are incorrect because they are not the longest national highways in Bihar.
- NH-31 is a 1,000-km-long highway that runs from Kolkata in West Bengal to Agartala in Tripura.
- NH-80 is a 760-km-long highway that runs from Delhi to Kanyakumari in Tamil Nadu.
- NH-57 is a 620-km-long highway that runs from Varanasi in Uttar Pradesh to Silchar in Assam.