Which of the Following Would Be Considered a Valid Informed

Which of the following would be considered a valid informed consent by a court?

A) Dr.Ambrose tells her patient in advance about a dangerous procedure and the risk involved,and obtains the patient's informed consent in writing on a form that is signed by the patient.
B) Dr.Ambrose tells her patient in advance about a dangerous procedure and the risk involved,and obtains the patient's informed consent in writing on a form that is signed by the patient and witnessed by a third party.
C) Dr.Ambrose obtains her patient's oral informed consent,which is witnessed by a third party.
D) Dr.Ambrose tells her patient the procedure is mandatory.