Step 1: Understanding the Concept:
International environmental and ecological commemorative days designated by the United Nations General Assembly.
Step 2: Detailed Explanation:
The United Nations General Assembly proclaimed March 21st as the International Day of Forests (World Forest Day) in 2012 to celebrate and raise global awareness of the importance of all types of forests and trees for sustainable development, climate moderation, and biodiversity conservation.
Step 3: Final Answer:
Thus, World Forest Day is celebrated on March 21st, corresponding to option (A).