I believe you are asking which of these answer options is the most fitting thesis statement. If this is the case, then I believe option C is the best answer. Even though not all of it is available, Ross seems to be asserting that the music that was becoming popular in the 1960s reflected the freedoms that society was beginning to get. This would be a good research statement because it is neither too broad nor too narrow, and it summarizes the main argument of his paper in a succinct way. Hope this helps.