Final answer:
The correct client form that allows clients to understand and accept the risks associated with beginning an exercise program is a liability waiver.
Step-by-step explanation:
The correct answer is B. Liability waiver. A liability waiver is a legal document that clients sign to acknowledge and accept the risks associated with starting an exercise program. It helps protect the fitness professional or facility from potential lawsuits in case of injuries or accidents. This form indicates that the client is aware of the risks involved and agrees to release the trainer or facility from any liability.