Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the best answer to each of the questions.

Today’s cars are smaller, safer, cleaner, and more economical than their predecessors, but the car of the future will be far more pollution-free than those on the road today. Several new types of automobile engines have already been developed than run on alternative sources of power, such as electricity, compressed natural gas, methanol, steam, hydrogen, and propane. Electricity, however, is the only zero-emission option presently available.

Although electric vehicles will not be truly practical until a powerful, compact battery or other dependable source of current is available, transport experts foresee a new assortment of electric vehicles entering everyday life: shorter-range commuter electric cars, three-wheeled neighborhood cars, electric delivery vans, bikes and trolleys.

As automakers work to develop practical electrical vehicles, urban planners and utility engineers are focusing on infrastructure systems to support and make the best use of the new cars. Public charging facilities will need to be as common as today’s gas stations. Public parking spots on the street or in commercial lots will need to be equipped with devices that allow drivers to charge their batteries while they stop, dine, or attend a concert. To encourage the use of electric vehicles, the most convenient parking in transportation centres might be reserved for electric cars.

Planners foresee electric shuttle buses, trains, buses and neighborhood vehicles all meeting at transit centres that would have facilities for charging and renting. Commuters will be able to rent a variety of electric cars to suit their needs: light trucks, one-person three-wheelers, small cars, or electric/gasoline hybrid cars for longer trips, which will no doubt take place on automated freeways capable of handling five times the number of vehicles that can be carried by freeway today.

Traveling in big cities is becoming more and more______ every day. (TROUBLE)