The primary mode of road transport for public commute in Bihar is:

The correct answer is: a) Buses.

Buses are the primary mode of road transport for public commute in Bihar. They are the most affordable and accessible mode of transport, and they connect all parts of the state. Buses are also the most popular mode of transport for long-distance travel.

Taxis are also a popular mode of transport in Bihar, but they are more expensive than buses. Taxis are usually used for short-distance travel or for getting to and from the airport.

Rickshaws are a traditional mode of transport in Bihar, but they are not as popular as they used to be. Rickshaws are usually used for short-distance travel within cities.

Metro trains are not available in Bihar.