Question

Cities grew along railroads and canals because
Answer

workers could not live anywhere else

the government designed the cities

there were not enough roads made of tar

settlers could obtain cheap land nearby

Answer 1

Is this question about US/Canadian history?

The answer is most likely "settlers could obtain cheap land nearby". As settlers moved west, the rails and canals were their link to the East, where they could get supplies shipped in or send out their grain, resources, and produce.

Workers could live further from rails, like on farms, so this doesn't make a lot of sense

The Federal governments did not design cities. Municipal governments oversee expansion of cities, but the city would be next to the rail in the first place, because of answer D

Roads aren't always made of Tar. Gravel, concrete or dirt roads were also used.