Final answer:
The two cities connected by the rail line that hosted the first passenger trains in the world are Manchester and Liverpool.
Step-by-step explanation:
The first passenger trains in the world traveled between Manchester and Liverpool. This pioneering rail line, established in 1830 during the Industrial Revolution, marked a significant milestone in transportation history. The two cities were important industrial centers in England with Manchester being a hub for industrialization and Liverpool serving as a port city, providing access to international markets and raw materials.