The correct answer is option 'D', world of green forests. Aunt's tigers belong to the natural habitat of green forests. Let's delve into the details to understand why.

Natural Habitat of Tigers
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Tigers are large, solitary cats that are native to various parts of Asia, including countries like India, Bangladesh, Nepal, and Bhutan. They are known for their majestic appearance and powerful presence in the wild. Tigers are primarily found in dense forests, grasslands, and mangrove swamps, where they can camouflage themselves and hunt effectively.

Importance of Green Forests for Tigers
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1. Shelter and Camouflage: Tigers are highly adaptable and have evolved to thrive in the dense vegetation of forests. The green foliage provides them with the perfect environment to hide, stalk prey, and blend in with their surroundings. The lush trees and dense undergrowth offer them shelter and protection from potential threats.

2. Prey Availability: Green forests are home to a variety of herbivorous animals, such as deer, wild boars, and antelope, which serve as the primary prey for tigers. The abundance of prey species in forest ecosystems ensures a stable food source for the tigers, allowing them to meet their dietary needs and survive.

3. Biodiversity Conservation: Forests play a crucial role in maintaining biodiversity. They provide a habitat for a wide range of plant and animal species, including those that are part of the tiger's natural prey. Preserving the green forests ensures the survival of not only tigers but also the entire ecosystem that relies on them.

4. Ecological Balance: Tigers are apex predators, meaning they are at the top of the food chain. By controlling the population of herbivores, they help maintain a balance in the ecosystem. This prevents overgrazing of vegetation and ensures the sustainability of the forest ecosystem.

Conservation Efforts
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Due to factors such as habitat loss, poaching, and illegal trade, tiger populations have drastically declined in recent years. To address this issue, various conservation organizations and governments have implemented measures to protect tigers and their natural habitats.

1. Protected Areas: Many countries have established national parks, wildlife reserves, and sanctuaries to safeguard the habitats of tigers. These protected areas help restrict human activities and provide a safe space for tigers to thrive.

2. Anti-Poaching Measures: Strict anti-poaching laws and enforcement efforts have been put in place to combat the illegal hunting of tigers for their body parts, which are highly valued in traditional medicine and the illegal wildlife trade.

3. Habitat Restoration: Efforts are being made to restore and reconnect fragmented forest habitats to create larger and more viable tiger landscapes. This involves reforestation initiatives, conservation planning, and community involvement in sustainable forest management.

Conclusion
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In conclusion, aunt's tigers belong to the world of green forests because that is their natural habitat. Green forests provide tigers with shelter, camouflage, prey availability, and contribute to the overall ecological balance. It is essential to conserve these forests and implement conservation measures to ensure the survival of tigers and the preservation of biodiversity.