Final answer:
The client should choose option C - "Taking calcium supplements isn't necessary." since it shows an understanding of the teaching.
Step-by-step explanation:
The client should choose option C. "Taking calcium supplements isn't necessary." This indicates an understanding of the teaching. While increasing intake of yogurt or including more cheese in the diet can provide calcium, these options may not be suitable for someone with an allergy to milk. Leafy green vegetables are a good source of calcium and can be included in the client's diet.