Sloping roofs are common in houses on mountains because they offer several advantages. Here is a detailed explanation of why sloping roofs are preferred for houses on mountains:

1. Protection against Snow and Rain:
- Sloping roofs are designed to shed snow and rain easily. The steep angle allows snow and rainwater to slide off quickly, preventing any accumulation that could potentially cause damage to the roof.
- Flat roofs, on the other hand, can accumulate snow and rain, leading to water leakage and structural issues.

2. Structural Stability:
- Sloping roofs are more structurally stable and can withstand the heavy weight of snow, which is common in mountainous regions.
- The angle of the roof helps distribute the weight evenly, preventing any excessive stress on the structure.
- Thatched roofs, which are made of straw or grass, may not provide enough structural stability and are more prone to damage in harsh weather conditions.

3. Efficient Drainage:
- Sloping roofs have a better drainage system as the water flows down the roof surface and into the gutters, preventing any waterlogging or damage to the house.
- Flat roofs, on the other hand, may have inadequate drainage systems, leading to water accumulation and potential leaks.

4. Aesthetic Appeal:
- Sloping roofs are visually appealing, especially in mountainous landscapes, as they blend well with the surroundings and create a sense of harmony.
- Thatched roofs and flat roofs may not complement the natural beauty of the mountains as effectively.

In conclusion, sloping roofs are the preferred choice for houses on mountains due to their superior protection against snow and rain, structural stability, efficient drainage, and aesthetic appeal. Thatched roofs and flat roofs are less suitable for mountainous regions due to their limitations in these aspects.

Introduction:
Houses on mountains have different types of roofs due to various factors such as weather conditions, architectural styles, and cultural influences. The correct answer to this question is option 'A', which states that houses on mountains have sloping roofs.

Reasons why houses on mountains have sloping roofs:
There are several reasons why houses on mountains typically have sloping roofs:

1. Snowfall:
Mountains are often prone to heavy snowfall. Sloping roofs allow the snow to slide off easily, preventing the accumulation of snow on the roof. This prevents the excessive weight of snow from damaging the structure of the house.

2. Rainfall:
Mountains also experience higher levels of rainfall compared to other areas. Sloping roofs help in channeling the rainwater away from the house, preventing water from seeping into the structure and causing damage.

3. Steep Terrain:
Mountains are characterized by steep terrains, and sloping roofs blend well with the natural landscape. The sloping roofs create a harmonious visual appeal and complement the overall aesthetics of the mountainous surroundings.

4. Structural Stability:
Sloping roofs provide better structural stability to houses on mountains. The angled design of the roof helps distribute the weight of the roof more evenly, reducing the strain on the walls and foundation of the house. This is particularly important in areas prone to landslides or earthquakes.

5. Architectural Style:
Sloping roofs are often a characteristic feature of the architectural style prevalent in mountainous regions. Many traditional designs and cultural influences incorporate sloping roofs as part of their heritage and identity.

Conclusion:
In conclusion, houses on mountains typically have sloping roofs due to factors such as snowfall, rainfall, steep terrain, structural stability, and architectural styles. Sloping roofs not only serve practical purposes like snow and water management but also contribute to the overall aesthetic appeal of the mountain houses.