Explanation:

- The World Health Organization (WHO) categorizes adolescents as individuals aged 10 to 19 years. This is a global standard that recognizes the transition from childhood to adulthood.

- Option 1: 10 to 19 years. This is the correct definition according to the WHO. It encompasses early to late adolescence, addressing various developmental stages.

- Option 2: 8 to 15 years. This range is too early and does not include late adolescents, missing some key developmental years.

- Option 3: 12 to 16 years. This range only covers a portion of adolescence, excluding older adolescents.

- Option 4: 6 to 14 years. This includes pre-adolescents and excludes mid to late adolescents.

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