Which of the following statements about Bond Duration is correct? Select one: a. The Modified Duration expresses the measurable change in the value of a security in response to a change in interest rates. b. The Modified Duration is the weighted average of time until all cash flows are received. c. The Modified Duration measures the amount of time required for the bond cash flows to cover the initial cost. d. The Modified Duration expresses the measurable change in the value of a security in response to a change in equity prices