The correct answer is: A. World Environment Day
World Environment Day is observed on June 5 every year. It is a United Nations observance day for encouraging worldwide awareness and action to protect the environment. The day was first celebrated in 1974 and is now coordinated by the United Nations Environment Programme (UNEP).
International Day of Non-violence is observed on October 2 every year. It is a day to commemorate the birth anniversary of Mahatma Gandhi, the leader of the Indian independence movement and a pioneer of non-violent resistance. The day was first celebrated in 2007 and is now observed by people all over the world.
Indian Air Force Day is observed on October 8 every year. It is a day to commemorate the establishment of the Indian Air Force in 1932. The day is celebrated with a flypast, parades, and other events.
United Nations Day is observed on October 24 every year. It is a day to commemorate the founding of the United Nations in 1945. The day is celebrated with speeches, concerts, and other events.