Research indicates that teenagers need more than nine hours of sleep for the best possible brain function. Teenagers who do not sleep enough can be irritable in school, perform badly on tests, and find it difficult to finish test questions.
We already established that this excerpt is about teenagers and is therefore for teenagers. We also can conclude that it was written for parents since it is that parent's responsibility to ensure that their child -- their teen gets enough rest. It's all about checks and balances. It also is helpful to teachers since the paragraph states that lack of adequate sleep for teens can drift off into their school life negatively.
Therefore, the answer is Choice A.