#25 - Mayor: Periodically an ice cream company will hold a

[Adam Tyson]

I agree with you, lounalola, that it is an intermediate conclusion of the argument, but answer C doesn't describe an intermediate conclusion, or any kind of conclusion. An intermediate conclusion is a statement that is supported by at least one premise, and which is also used as a premise to support another conclusion. Answer C specifically says that it does not support the main conclusion!

For an answer like C to be correct, it would have to describe some sort of background information. In this case, that answer seems to be describing this claim: "those who drive to work complain about the congestion they face in their rush-hour commutes." That's why the argument needs to be made, but it doesn't act as a premise in support of the claim that a system for charging people would reduce congestion.