Which is an example of a technology that fundamentally changed transportation systems historically?

The choice representing "all of the above" is correct because each of the technologies listed—subways, high-speed trains, and automobiles—has significantly transformed transportation systems at various points in history.

Subways revolutionized urban transit by providing efficient, high-capacity transportation beneath the streets, alleviating surface congestion and enabling rapid movement across cities. This mode of transport played a critical role in shaping modern urban environments and influenced where people live and work.

High-speed trains have fundamentally changed long-distance travel by providing a fast and efficient alternative to automobiles and airplanes. They have not only transformed intercity transportation, making it quicker and more accessible, but also contributed to sustainability by reducing reliance on fossil fuels and lowering greenhouse gas emissions.

Automobiles have had perhaps the most profound impact on transportation, reshaping cities, economies, and lifestyles. The advent of the automobile enabled personal mobility on an unprecedented scale and facilitated the expansion of suburbs and rural areas, changing how people commute and structure their daily lives.

Together, these technologies illustrate significant shifts in transportation systems, each contributing uniquely to the way society functions today. Their collective impact underscores the importance of technological advancements in shaping transportation, urban planning, and social structures.