The hilly terrain and frequent landslides can disrupt:

The correct answer is: Road and air transport.

Hilly terrain and frequent landslides can disrupt road and air transport by making roads impassable and runways unusable. This can lead to delays and cancellations of flights and other forms of transportation. In some cases, it may even be necessary to evacuate people from affected areas.

Rail and water transport are less likely to be disrupted by hilly terrain and landslides. However, they can still be affected if the landslides cause damage to bridges or other infrastructure.

Not a significant issue is not the correct answer because hilly terrain and frequent landslides can have a significant impact on transportation.