A consensus is typically a general agreement among a group. In this context, the sentence that best represents a consensus is:
C. It has been determined by the audience that solar panels rather than air-conditioners are the best way for the school to use its grant money.
This sentence indicates that a decision has been made by the audience as a group, suggesting a collective agreement on the matter. The other sentences either reflect personal opinions or are statements that do not indicate a group consensus.