The correct answer is: B. 9/11 Anniversary.
11 September is observed as the anniversary of the September 11 attacks, a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda against the United States on the morning of Tuesday, September 11, 2001. The attacks resulted in 2,977 fatalities, over 25,000 injuries, and substantial long-term health consequences, in addition to at least $10 billion in infrastructure and property damage. It is important to remember the victims of this tragedy and to work to prevent future acts of terrorism.
Option A is incorrect because World Day for War Orphans is observed on 6 June.
Option C is incorrect because World Day of Theatre for Children and Young People is observed on 20 November.
Option D is incorrect because World Suicide Prevention Day is observed on 10 September.