The correct answer is: Only assumption I is implicit.
The statement is an advertisement for X-T.V., which states that the only way to buy an X-T.V. is to contact Y, the sole agent of X-T.V. This does not necessarily mean that people generally prefer to buy T.V. through sole agents. It is possible that Y is the only place to buy X-T.V., or that Y offers a better deal than other retailers. Additionally, the statement does not say anything about whether or not T.V. producing companies sell their products directly. It is possible that they do, but that Y is the only authorized retailer of X-T.V.
Therefore, only assumption I is implicit in the statement.