The correct answer is C, Prohibit the student from entering any type of transaction for the account. Under the Uniform Transfers to Minors Act (UTMA), the account is legally owned by the minor, but only the custodian has authority to manage and control the account. The minor (in this case, a 17-year-old student) does not have legal capacity to enter into securities transactions, regardless of any permission granted informally by the custodian.

From a regulatory standpoint, broker-dealers and registered representatives must follow strict rules regarding account authority. Even if a custodian tells the minor they may trade, this does not override legal requirements. The RR may only accept instructions from the custodian, who is the legally authorized party.

Choices A and B are incorrect because no documentation can grant trading authority to a minor—this would violate securities regulations and contract law principles. Choice D is unnecessary because the issue is not lack of approval, but lack of legal authority.

Therefore, the RR must refuse the order and only accept trading instructions from the custodian, making choice C the correct and compliant action.