It's called that because it was one of the first streets in New York City to be lit with electric lights. People continue to use this term today because the millions of lights on the theatre marquees still brighten up the night sky in a flashing white.
B should be the correct answer
The answer would be A. became
A coordinating conjunction joins words, phrases or clauses having similar grammatical structure. A coordinating conjunction is also called a coordinator, which are 'but, and, or, so, nor, yet, for'.
B - too specific for the purpose
While that would be a good topic sentence, it is far too specific for the thesis of an entire essay