Which action invalidates the contract Tim signed with the rental agency?

The following section is a statement from the rental agreement Tim signed when he rented his car this past weekend.
“Upon checkout, the fuel level of the vehicle will be determined by turning the vehicle on and visually inspecting the fuel gauge. The approximate fuel level will be recorded on the Check-Out sheet and verified with initials by the vehicle Renter. One copy of the Check-Out sheet will be given to the customer. Another copy will be kept with the on-site records of the vehicle.
The rented vehicle must be returned with a minimum fuel level the same as that indicated on the Check-Out sheet. A vehicle returned with a fuel level less than the approximate level indicated on the Check-Out sheet will be completely refueled with on-site pumps. The price of the fuel used to refuel the vehicle will be added to the Renter’s total charge at a cost of $4.50 per gallon plus a $5.00 re-fueling charge.”
As a part of the check-out process, it is customary for a car rental agency to look over the car with the customer and fill out the Check-Out sheet together. As Tim was walking around the car looking for damages that he didn’t want to be held responsible for, the agency representative turned on the car, took note of the fuel level, and indicated it on the Check-Out sheet. Since Tim didn’t have any questions, the clerk handed him the keys and a copy of the Check-Out sheet and wished him well.
Which action invalidates the contract Tim signed with the rental agency?
a.
Tim failed to notice a dent under the right front fender.
b.
The representative failed to give Tim a copy of the Check-Out sheet.
c.
The representative failed to have Tim initial by the fuel level on the Check-Out sheet.
d.
Neither Tim nor the representative checked the oil level in the car.