Task: Question Generation
Input (English): Background Paragraph: Gasoline-powered vehicles emit a lot of harmful materials. Nitrogen oxides are formed when atmospheric nitrogen reacts with oxygen at the high temperatures found in a car engine. Carbon monoxide is a by-product of incomplete combustion of hydrocarbons. Evaporated and unused fuel releases volatile hydrocarbons into the atmosphere to help form smog. The presence of a catalytic converter in the exhaust system of the car causes these materials to react and be changed into less harmful products. 
Story: Berg city used only gas powered vehicles while Hill city used electrical vehicles. The two cities had a similar population and vehicle numbers.
Output (English): Which city had more problems with nitrogen oxides?