参考答案：A

解析：

If bonds are identical except for the coupon rate, the one with the lowest coupon will exhibit the most price volatility. This is because a bond's price is determined by discounting the cash flows. A lower-coupon bond pays more of its cash flows later (more of the cash flow is comprised of principal at maturity) than a higher-coupon bond does. Longer-term cash flows are discounted more heavily in the present value calculation.