The correct answer is option 'B'. Evergreen forests are called so because they remain green throughout the year. Let's understand in detail why this is the case.

What are Evergreen Forests?
Evergreen forests are a type of forest ecosystem characterized by the presence of trees that retain their green foliage all year round. These forests are found in regions with high rainfall and relatively warm temperatures. They are typically located in tropical and temperate regions around the world.

Why do Evergreen Forests remain green throughout the year?
There are several reasons why evergreen forests remain green throughout the year. These factors contribute to the continuous presence of green foliage in these forests:

1. Climate: Evergreen forests are found in regions with high rainfall and warm temperatures. The combination of abundant rainfall and consistent warmth provides favorable conditions for plant growth. The availability of water and sunlight throughout the year allows the trees to maintain their green foliage.

2. Leaf Structure: The leaves of trees in evergreen forests are specially adapted to withstand harsh climatic conditions. They have thick waxy coatings and needle-like structures that help reduce water loss through evaporation. These adaptations allow the trees to retain their green leaves even during dry periods.

3. Continuous Photosynthesis: Photosynthesis is the process by which plants convert sunlight into energy, using carbon dioxide and water. Evergreen trees have a continuous process of photosynthesis throughout the year. This is possible because they do not shed all their leaves at once, unlike deciduous trees. As a result, they can produce food and retain their green foliage even during the winter months.

4. Species Diversity: Evergreen forests are often characterized by a wide variety of tree species. Each species may have different growth and adaptation strategies to ensure the continuous presence of green foliage. This diversity contributes to the overall resilience and greenness of the forest ecosystem.

In conclusion, evergreen forests remain green throughout the year due to favorable climatic conditions, specialized leaf structures, continuous photosynthesis, and species diversity. These factors enable the trees to retain their green foliage and contribute to the lush and vibrant appearance of these forests.