The second sentence shouldn't start with Since because Since is a word to combine sentences like because combines sentences. They are conjunctions I believe.
The answer is C because "since" is a subordinating conjuction, it can be in two places in a sentence. After a comma (He had to get her a present, since it was her birthday.), or it can be at the beginnning, but when a subordinating conjunction is at the beginning of a sentence, it makes the part of the sentence before the comma a dependent clause. In order to correctly write the sentence, you would need to provide an independent clause after the dependent clause.
That is because it is often associated with oppression and history that followed it. According to Baldwin, there's a thing called Black English that often becomes a part of the General American English and he provides the word Jazz as an example of something that used to be sexual but is now changed into a musical thing. <span />
