Explanation:

Mangrove forests are unique ecosystems that thrive in saline coastal environments, characterized by wet, marshy, and deltaic soils. These trees have specialized root systems (like prop roots and pneumatophores) that enable them to adapt to waterlogged, anaerobic conditions and fluctuating tides. Option B, Fir trees, are typically found in cold, temperate regions with well-drained soils. Option C, Cactus, are desert plants adapted to arid conditions and sandy soils. Option D, Oak trees, generally grow in temperate forests with various soil types but not typically marshy, saline deltaic soils. Thus, mangroves are perfectly suited for such environments.