Who has legal authority to consent to a child's medical treatment if the parent is unavailable?

The correct response reflects the principle that medical consent for a minor typically requires a legally recognized individual, such as a parent or legal guardian. In situations where the parent is unavailable, an adult with written authorization from the parent has the legal authority to consent to medical treatment for the child. This authorization ensures that the adult acting on behalf of the parent has the parent's consent and can make informed decisions regarding the child's medical needs.

Other options, such as a neighbor, friend, or unrelated adult without the appropriate written authorization, do not have the legal standing to consent to medical treatment for a child. This is based on the need for clear and formal consent to ensure the child's welfare and legal protections.