C. Cable TV channels also have as many advertisements as free TV channels.
Feedback Choice (a) supports the salesman's statement. It states that those who do not watch TV tend to spend less. This supports the salesman's statement.
Choice (b) is referring to the TV signals but not about advertisements. Hence, (b) is out of context.
Choice (c) states that the cable TV channels also allow advertisements as much as free TV. Since the salesman has pointed out that advertisement make viewing of free TV indirectly costly, the same is applicable to cable TV as well.
Hence, (c) goes against the statement of the salesman.
According to choice (d) people get access to some free TV channels also. But it is not clear whether those few free channels have advertisements.
Hence, (c) does against the statement of the salesman.