The correct answer is option 'B' - International Union for Conservation of Nature and Natural Resources.

The International Union for Conservation of Nature and Natural Resources (IUCN) is an international organization that aims to promote the conservation and sustainable use of nature and natural resources. It is the world's largest and most diverse environmental network, with members from governments, non-governmental organizations, and indigenous peoples' organizations.

Below are some key details about IUCN:

1. Establishment: The IUCN was established in 1948. It was initially known as the International Union for the Protection of Nature (IUPN) and later changed its name to the International Union for Conservation of Nature and Natural Resources in 1956.

2. Mission: IUCN's mission is to influence, encourage, and assist societies around the world in the conservation of nature and ensuring the sustainable use of natural resources.

3. Objectives: The organization has several objectives, including:
- Promoting the establishment and management of protected areas.
- Promoting the conservation and sustainable use of biodiversity.
- Influencing policies and practices to ensure the sustainable use of natural resources.
- Promoting the equitable and sustainable management of water resources.
- Addressing the impacts of climate change on ecosystems and biodiversity.
- Supporting the conservation and management of species at risk of extinction.

4. Red List of Threatened Species: One of IUCN's notable initiatives is the development and maintenance of the Red List of Threatened Species. This list assesses the conservation status of various species and provides valuable information for conservation planning and decision-making.

5. Programs and Projects: IUCN carries out numerous programs and projects worldwide to address various conservation challenges. These include initiatives related to ecosystems, species, climate change, protected areas, sustainable development, and more.

6. Partnerships and Collaboration: IUCN works collaboratively with governments, NGOs, indigenous communities, and other stakeholders to achieve its conservation goals. It facilitates knowledge sharing, capacity building, and policy advocacy to promote effective conservation action.

In conclusion, the International Union for Conservation of Nature and Natural Resources (IUCN) is a global organization dedicated to conserving nature and promoting sustainable use of natural resources. It plays a crucial role in influencing policies, conducting research, and implementing conservation initiatives to protect biodiversity and ecosystems worldwide.