Final answer:
Consent must be obtained before the treatment begins to ensure that participants are fully aware of what they are consenting to. Correct option is C.
Step-by-step explanation:
Informed consent is the process by which individuals voluntarily agree to participate in a study or treatment after being provided with all the necessary information. According to the information provided, consent must be obtained before the treatment begins. This ensures that participants are fully aware of what they are consenting to and have the opportunity to ask questions or clarify any concerns before the treatment or study starts.