Explanation:

- Option 1: Boys - While the issue of suicide could be relevant, the term "boys" is gender-specific and doesn't encompass all young people.

- Option 2: Infants - This is not appropriate since infants are too young to face the complexities of depression and suicide.

- Option 3: Girls - Like "boys," this is gender-specific and doesn’t include the broader group of young people who could be affected.

- Option 4: Adolescents - This is the most suitable word to fill in the blank. It describes a broader age group, including all genders who may face depression and are at risk of suicide.