All other things equal, which of the following would be most sensitive to a $1\%$ change in the interest rate?

a$.$ A $30$ year bond with a $10\%$ coupon, trading at discount

A has higher yidd than is

b$.$ A $30$ year bond with a $10\%$ coupon, trading at premium

:$.B$ is mon semsitive than A

c$.$ A $30$ year bond with a $9\%$ coupon, trading at par

d$.$ A $30$ year zero coupon bond

to compan b witt $c$ I read lie yicld.