The correct option is D Trees are planted along slopes to form natural barriers.
The following measures can be taken to mitigate the effects of landslides:
1. Do not construct houses or buildings near areas where landslides are common.
2. Planting trees on hill slopes can reduce landslides as they form a natural barrier to the landslides.
3. Tall and gigantic walls should be built along the slopes of the hills to block the debris of the landslide falling onto the roads and houses.
4. Water pipes, electric lines and telephone lines must be fitted underground in these areas to avoid damage.