7. 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 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?
A. The side windows had no ice condensation on them
B. 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.
C. The speed at which ice on a window melts increases as the temperature of the air blown on the window increases
D. The warm air from the defrosting vent for the front windshield cools rapidly as it dissipates throughout the rest of the car.
E. 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.
7.
The speed with which the ice on the windshield melted is attributed to the air blowing full force from the defrosting vent onto the front windshield. This explanation of B is undermined if, as B states, no attempt was made to defrost the back window and the ice on the back window melted as quickly as did the ice on the windshield. Therefore, B is the best answer.
In the absence of other information, the lack of ice condensation on the side windows that is mentioned in A is irrelevant to the validity of the explanation. C might support the explanation, since the air from the defrosting vent was warm. Neither of D and E gives a reason to doubt that air from the vent caused the ice’s melting, and thus neither jeopardizes the explanation’s validity.
谁能解释一下这题为何选B？ | 
