In the United States, the Postal Service has a monopoly on first-class mail, but
    much of what is sent first class could be transmitted electronically. Electronic transmittal operators argue that if the Postal Service were to offer electronic transmission, it would have an unfair advantage, since its electronic transmission service could be subsidized from the profits of the monopoly.

(A) Is the Postal Service as efficient as privately owned electric transmission services?

(B) If private operators were allowed to operate first-class mail services, would they choose to do so?

(C) Do the electronic transmittal operators believe that the Postal Service makes a profit on first-class mail?

(D) Is the Postal Service prohibited from offering electronic transmission services?（C）

(E) Is the Postal Service expected to have a monopoly on electronic transmission?

答案是C，不太明白。

since its electronic transmission service could be subsidized from the profits of the monopoly.

这句话的意思就是Postal Service 用first-class mail赚的钱来补助electronic transmission service，就是说它在first-class mail是赚钱的。

所以就是C的答案了。