已知｜a｜＝4,｜b｜＝8，a与b的夹角为120°，则｜2a-b｜＝ .
810÷80﹦10…10______．
Which of the following statements about the role of the marginal cost of capital in determining the net present value of a project is most accurate The marginal cost of capital should be used to discount the cash flows:（）
A. if the firm’s capital structure is expected to change during the project’s life.
B. of all projects the firm is considering.
C. for potential projects that have a level of risk near that of the firm’s average project.
