Which of the following statement is (are) true with respect to yield curve risk?

I. The effective duration of a portfolio is simply the sum of the duration of each of the individual bonds in the portfolio.
II. The effective duration of a portfolio indicates by what percent the portfolio value will change as a result of a change in the yield curve.
III. Key rate duration measures how much the portfolio value will change given a yield change for only one specific maturity.
IV. For a given portfolio, the rate duration will be the same for every maturity along the yield curve.

Explanation: I is not entirely true because the effective duration of a portfolio is the weighted average of the duration of each of the individual bonds, with the weights being equal to the bond's market value as a proportion of total portfolio value.

II is not entirely true either because effective duration of a portfolio indicates by what percent the portfolio value will change as a result of a "parallel" shift in the entire yield curve. A parallel shift would mean that interest rates at all different terms would have to change by the same amount, a rare occurrence indeed.

IV is incorrect because for a given portfolio, the rate duration will be different for every maturity along the yield curve.