Which of the following statements regarding capital budgeting is correct A firm’s optimal capital budget can be found by moving along its investment opportunity schedule until: （）

A. it exhausts its capital budget. 

B. the marginal revenue product is equal to marginal cost. 

C. the next project’s return no longer covers the marginal cost of capital.

根据《万国邮政公约》的规定，以可负担得起的价格在领土的每一个角落提供经常、优质的基本邮政业务，指的是( )。

A．邮政运营者的法律地位
B．邮政安伞
C．邮政资费
D．普遍服务