Final answer:
Most engines in modern cars have replaced carburetors with fuel injection systems to improve fuel economy and reduce emissions. Catalytic converters and advances in engine technology also contribute to cleaner and more efficient cars. The correct answer is B.
Step-by-step explanation:
The majority of modern engines in today's cars have replaced the carburetor with fuel injection systems. Unlike carburetors that mix fuel and air in the intake manifold, fuel injection precisely meters the fuel directly into the combustion chamber or intake tract. This results in more efficient fuel use, improved fuel economy, and reduced emissions. Innovations such as computerized engine controls, variable valve timing, and gasoline direct injection have further improved the efficiency and environmental performance of internal combustion engines.
Furthermore, devices such as three-way catalytic converters have been crucial in reducing pollutants like hydrocarbons, nitrogen oxides, and carbon monoxide by converting them into less harmful substances like dinitrogen, oxygen, carbon dioxide, and water vapor. These converters typically contain a platinum-rhodium catalyst that facilitates these reactions. Advances in engine technology and fuel standards, including unleaded gasoline and low sulfur levels, have significantly decreased emissions that contribute to air pollution and smog.
In contrast to fuel injection, technologies like turbo-chargers are used to increase engine power and performance by forcing more air into the engine's combustion chamber, while catalytic converters and advanced transmission technologies such as 7+ speeds, dual clutch transmissions (DCTs), and continuously variable transmissions (CVTs) aid in reducing emissions and raising fuel efficiency. Ram-air induction is also a performance enhancement feature that uses the force of moving air to increase air intake and thereby engine power, but it is not a replacement for the carburetor.