GMAT Sentence Correction (SC) | Re: In La Plata, Argentina, one of the first cities

First, The initial portion of the sentence(In La Plata, Argentina, one of the first cities to offer complimentary wireless Internet access to the public) is not a clause - it is a prepositional phrase: there is no verb in this part.

Moreover even if the first portion were a clause, there is no issue with the second portion being an independent clause:
Although I tried hard, I lost. (I lost is an independent clause - "used after a clause and separated with only a comma" - nothing