960 - Logical Reasoning

Question1 : The ice on the front windshield of the car had formed when moisture condensed during the night. The ice melted quickly after the car was warmed up the next morning because the defrosting vent, which blows only on the front windshield, was turned on full force.
Which of the following, if true, most seriously jeopardizes the validity of the explanation for the speed with which the ice melted?

1. The side windows had no ice condensation on them.
2. Even though no attempt was made to defrost the back window, the ice there melted at the same rate as did the ice on the front windshield.
3. The speed at which ice on a window melts increases as the temperature of the air blown on the window increases.
4. The warm air from the defrosting vent for the front windshield cools rapidly as it dissipates throughout the rest of the car.
5. The defrosting vent operates efficiently even when the heater, which blows warm air toward the feet or faces of the driver and passengers, is on.