Which One of the Following Is the Reason That Macaulay

Which one of the following is the reason that Macaulay duration is NOT a good measure of interest rate risk for mortgage bonds?

A) Mortgage bonds are long-term securities while Macaulay duration is a short-term measure.
B) Macaulay duration assumes the debt has a variable rate and most mortgages have a fixed rate.
C) Macaulay duration requires bond payments to be made semiannually.
D) Macaulay duration assumes payments are fixed and mortgage bond payments vary.
E) Macaulay duration only applies to zero coupon bonds.