Final answer:
An unconscious patient whose life is in danger can receive invasive medical treatment without a signed consent form, as life-saving treatments can be performed under the principle of implied consent during emergencies.
Step-by-step explanation:
The individual who can receive invasive medical treatment without a signed consent form is: B. An unconscious patient whose life is in danger. In emergency situations, if a patient is unconscious and unable to give consent, medical professionals are permitted to administer necessary treatment to save the patient's life under the principle of implied consent. This scenario falls under the category of nonvoluntary passive euthanasia, where treatment can be provided without the explicit consent of the patient because the individual is not in a state to make that decision. However, in all non-emergency situations, valid informed consent must be obtained before any invasive procedure. This includes a thorough understanding of the procedure, and its potential risks and benefits, which patients must acknowledge, often in the presence of witnesses.