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

Multiple Choice

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

B $20-$year bond with a $10\%$ coupon yielding $11\%$

C $20-$year zero$-$coupon bond yielding $10\%$

D $21--$year bond with a $10\%$ coupon yielding $10\%$

I tried to put the answer D but using the check mode it's incorrect so the correct one is between the A$,$B$,$C$.$ give me the correct solution, please. thanks.

then, we have:

The historical yield spread between the AA bond and the AAA bond has been $25$ basis points. Currently the spread is only $9$ basis points. If you believe the spread will soon return to its historical levels,

you should

Multiple Choice

A$.$buy the $AA$ and short the AAA

B$.$buy both the $AA$ and the AAA

C$.$buy the AAA and short the AA

D$.$short both the $AA$ and the AAA

in the second question i tried to put the answer A but it is incorrect $.$ give me the right solution, thanks.