Which of the Following Is Not a Weakness of Duration

Which of the following is not a weakness of duration gap analysis?

A) It is difficult to accurately compute duration.
B) Each future cash flow must be discounted by the appropriate future interest rate.
C) The duration of a portfolio must be constantly monitored.
D) It is difficult to estimate the duration on zero coupon bonds.
E) All of the above are weaknesses of duration gap analysis.