18. A entered into a contract of sale conveying a house and lot in favor of B. Unwilling to pay thousands of pesos for notarization fees, A and B decided not to have the contract of sale notarized. B nonetheless made C, her nephew, a 2nd year law student, check the contract. C informed his aunt that the sale was void because it was not in a public instrument. He thus advised her to file a case in court to declare the contract of sale void. Is C correct? Reason(s).