If a car's is malfunctioning, people in the car will become ill when driving long distances, especially if the windows are closed.

If a car's A/C air conditioning system  is malfunctioning

Explanation:

When the Air conditioning system of a car is malfunctioning the car will become extremely hot especially when the windows are closed and the car is driving long distance and this might lead to heat stroke for the occupants of the car if the heat becomes extreme to bear.

when driving with the windows open,the inside of the car won't be so hot as with when the windows are closed this is regardless if the A/C system of the car is malfunctioning or not.

the anwser is ethier d or e