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 because they can make roads impassable and runways unusable. This can lead to delays and cancellations of flights and other forms of transportation.

Rail and water transport are less likely to be disrupted by hilly terrain and landslides because they are not as dependent on roads and runways. However, they can still be affected by landslides if they occur near railway tracks or waterways.

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