An older boy and a younger boy doesn't imply that they are brothers.
This justifies what answer for what question? Q & A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Given the sentence "An older boy drinks from a water fountain while a younger boy watches." can we conclude that "The boys are brothers."?
Options:
- yes
- it is not possible to tell
- no
it is not possible to tell