All other things equal, which of the following has the longest duration?

A$)$ A perpetual bond paying a $12\%$ coupon and yielding $6\%.$

B$)$ A $20$ year bond with a $10\%$ coupon yielding $10\%$

C$)$ A $20$ year bond with a $10\%$ coupon yielding $11\%$

D$)$ A perpetual bond paying a $6\%$ coupon yielding $8\%$