The correct option is A. This group contains species that are either Endangered or Critically Endangered according to the IUCN Red List and are high-priority conservation species in India.

• Great Indian Bustard: Critically Endangered. It is one of the heaviest flying birds and is found mainly in Rajasthan and Gujarat.
• Musk Deer (Himalayan Musk Deer): Endangered. It is hunted for its musk pod and faces habitat loss in the Himalayan region.
• Red Panda: Endangered. It is native to the eastern Himalayas and southwestern China.
• Asiatic Wild Ass (Khur): Near Threatened (IUCN), but it is listed under Schedule I of the Wildlife Protection Act, 1972, and is considered a highly threatened species in the Indian context.

Options B, C, and D are incorrect because they include species categorized as 'Least Concern' by the IUCN, which disqualifies the entire group from being classified as 'endangered':

• Cheetal (Spotted Deer): Least Concern (found in Options B and D).
• Blue Bull (Nilgai): Least Concern (found in Options B and D).
• Rhesus Monkey: Least Concern (found in Option C).
• Hanuman Langur: Least Concern (found in Option D).
• Additionally, species like the Saras Crane and Swamp Deer (Option C) are categorized as Vulnerable, not Endangered.