An investor is considering the purchase of two bonds. One of the bonds is tax-exempt and yields 4.5% while the other bond is taxable and yields 6.0%. If the two bonds are alike in all other characteristics, the marginal tax rate that would make the investor indifferent between the two bonds is closest to:（）

A. 9.0%.

B. 25.0%.

C. 27.0%.

以下卧式注射机操作中（）项操作无误。

A.用手触摸热电部分以判断工作正常

B.从后安全门取出成品或维修模具以保证操作安全

C.操作时后安全门可以打开

D.操作时不要乱动各行程开关和安全开关