Which statement describes a cultural opportunity that became available as cities grew in the late 1800s?
a. city dwellers could visit museums.
b. city dwellers could attend schools.
c. city dwellers could work in factories.
d. city dwellers could travel on transit systems.

The key word in  the question is "cultural" , as in "cultural opportunity".

Transit systems, factories and even schools are not cultural opportunities, but museums are - that's why a) is the correct answer.

And there were already museums in 1800 - for example Rijksmuseum in the Netherlands.