Final answer:
The main idea of the provided excerpt discusses the challenges and potential improvements that can be made to the city's transportation system in the U.S. urban landscape, including reducing emissions, efficient fuel usage, and promoting public transport to make it more accessible. The correct option is option C.
Step-by-step explanation:
To determine the main idea of the excerpt given, we must look for recurring themes and overarching messages within the text snippets provided. From the information about transportation systems, urban planning, environmental concerns, and suggestions for improving public transport usage, it's clear that the excerpt focuses on the challenges and potential solutions related to urban transportation systems.
Based on the details mentioned about the importance of urban planning, the high percentage of emissions from cars, and suggestions for encouraging public transport to save money and reduce environmental impact, we can infer that the main idea revolves around improving the transportation system. While options A and B talk about comparisons between cars and trains or Americans with citizens from other countries, and option D is incomplete, it is option C, 'The transportation system the city proposes should be improved,' that captures the essence of the excerpt.
Using urban planning to mitigate transportation emissions, encouraging the use of less carbon-intensive fuels, and promoting public transport like buses or free rides to school are some of the solutions alluded to in the excerpt. Such solutions aim to increase efficiency, decrease environmental damage, and make transportation more accessible for everyone.
Therefore, based on the information provided, the correct option for the main idea of the excerpt is option C.