Answer:
The most effective way to combine those sentences is A. A lot of teens express themselves through fashion, and since many teens start earning their own money, they can buy their own clothes and choose the fashions that they want.
Explanation:
Option A is the most effective way to combine those two sentences because is demonstrates a coordinating relationship between sentence 11 and 12 and, at the same time, introduces a reason through the conjunction since. Moreover, option A is punctuated correctly because it contains a comma before a coordinating conjunction linking two independent clauses and another one that separates a dependent clause from an independent clause.
