Concept:August 12 is globally observed as International Youth Day, as declared by the United Nations.
Explanation:The UN General Assembly endorsed the recommendation in 1999 and officially designated August 12 as International Youth Day.
The day was first celebrated on August 12, 2000.
It aims to recognize youth contributions and encourage their active participation in society.
Other important days mentioned in the options have different dates:
World Environment Day is June 5.
World No-Tobacco Day is May 31.
International Day against Drug Abuse and Illicit Trafficking is June 26.
Hence, only the date August 12 corresponds to International Youth Day.
Answer:D. International Youth Day