The mayor has been accused of taking a bribe based on the fact that a consultant that does business with the city paid for improvements to the mayor's vacation house.
Opposing Evidence
A consultant that does business with the city paid for improvements to the mayor's vacation house.
Opposing Conclusion (Accusation)
The mayor took a bribe.
Mayor's Evidence
He (the mayor) paid every bill for those improvements that was presented to him.
Mayor's Conclusion
He did not take a bribe.
Evaluate
We're told that the mayor has been accused of taking a bribe, and then given a statement that the mayor makes "in his own defense." We can infer that the mayor is denying the accusation that he took a bribe.
The mayor is denying this by stating that he paid every bill "that was presented to him." Okay... what if some bills were never presented to the mayor because the consultant paid those bills?
If the mayor knew the consultant was doing that, the mayors defense is weakened. The consultant would potentially be bribing the mayor with improvements to the vacation house instead of giving the mayor money directly.
Goal
A correct answer might indicate that this was the situation: the mayor was aware that some bills were never presented to him and were instead paid by the consultant.