Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Rebetiko, initially a music associated with the lower classes, later (and especially after the population exchange between Greece and Turkey) reached greater general acceptance as the rough edges of its overt subcultural character were softened and polished, sometimes to the point of unrecognizability. It was the base of the later laïkó (song of the people). The leading performers of the genre include Apostolos Kaldaras, Grigoris Bithikotsis, Stelios Kazantzidis, George Dalaras, Haris Alexiou and Glykeria.
What music began associated with the lower classes?