On opening day, officials quickly realized the new subway system was not enough to relieve overcrowding in the city. Which sentence from the text explains why?
A The city would own the system, and Belmont would construct it for $35 million.
B The streets hummed with more than 100,000 people making their way to the subway for a five-cent ride.
C In an age before machines, workers used picks and shovels during construction of the subway.
D In the end, this first phase of the subway’s construction employed between 7,000 and 12,000 laborers.