Final answer:
The participant's mistakes in CPR technique could be not keeping their arms straight, not placing the hands in the center of the chest, and incorrect hand positioning. All these factors are important for effective and safe CPR.
Step-by-step explanation:
The participant may be making several possible mistakes while performing CPR. d. All of the above are possibilities for the mistakes a participant can make, which include: a. Not keeping their arms as straight as possible, which is essential for proper force transfer; b. Not putting the hands in the center of the manikin's chest, which is the correct position to compress the heart effectively; and c. Not putting their arm over their hands, which could mean that the hands are not positioned one on top of the other in the correct manner. These techniques are crucial as improper hand placement or arm posture can result in ineffective chest compressions or even injury to the patient.