The correct answer is: b) Frequent landslides.
Mizoram is a state in north-eastern India that is prone to landslides. The state has a hilly terrain and is located in the Himalayas, which are a mountain range that is prone to earthquakes. Landslides are a major challenge for road transport in Mizoram because they can block roads and make it difficult or impossible for vehicles to pass. Landslides can also damage bridges and other infrastructure, which can further disrupt road transport.
The other options are not as significant challenges for road transport in Mizoram. Traffic congestion is a problem in some parts of the state, but it is not as widespread as in other parts of India. Limited parking space is a problem in some urban areas, but it is not as severe as in other major cities in India. Poor road quality is a problem in some parts of the state, but it is not as widespread as in other parts of India.
In conclusion, the major challenge for road transport in Mizoram is frequent landslides. Landslides can block roads, damage bridges and other infrastructure, and make it difficult or impossible for vehicles to pass.