i believe the answer is: Fuel filter
Fuel filter is a part of your vehicles that screens out various form of small particles from the fuel (such as dirts). Every 15,000 miles, there would be a chance that your fuel filter is clogged. If this fuel filter is not changed, it would be hard for you to start your car.
I can give you my take on it:
In command economies the quantity and more importantly the prize of the products is decided by the government and not by the people in production. As a result, people in the production can't have the motivation of producing more, as they won't benefit from it. So command economy encourages low motivation among the workers (i believe this was the case in the Eastern Block)
An ionic solution would be able to conduct electricity where as the covalent would not so if you have a conductivity tester which are available in most labs you should be able to distinguish between the 2
It seems that Linda is suffering from anxiety or a panic attack. The theory of emotion would be anxiety.