highgmat logic 2

Local phone companies have monopolies on phone service within their areas.
Cable television can be transmitted via the wires that are already in place and
owned by the phone companies. Cable television companies argue that if the
telephone companies were to offer cable service, these telephone companies would
have an unfair advantage, because their cable trasmissions could be subsidized by
by the profits of their monopolies on phone service

on the basis of the information provided in the passage above, which of the following
questions can be answered?

B if phone companies were allowed to provide cable service, would they want to do so?
C do the cable companies believe that the local phone companies make a profit on phone
service?
D Are local phone companies forbidden to offer cable service?
E is it expected that phone companies will have a monopoly on cable service?

choose C

I don't understand why "their cable trasmissions could be subsidized by
by the profits of their monopolies on phone service"can cause "these telephone companies would have an unfair advantage"

telephone companies 得到subsidize 就可以降低价格，所以才会占优势地位？