SC-In La Plata, Argentina

[CHUNX638]

In La Plata, Argentina, one of the first cities that was offering the public complimentary wireless Internet access; anyone with a wireless-enabled device can access the Internet from virtually any location in the downtown area.
A. that was offering the public complimentary wireless Internet access; anyone with a wireless-enabled device can
B. has offered complimentary wireless Internet access to the public; with a wireless-enabled device, anyone can
C. to offer complimentary wireless Internet access to the public, anyone with a wireless-enabled device may
D. offering the public complimentary wireless Internet access, enabling anyone with a wireless-enabled device to
E. offers to the public complimentary wireless Internet access, which, with a wireless-enabled device, allows anyone to

Explanation: The idiomatic construction one of the first to is used correctly.
I don't know why this sentence need to use "one of the first cities to do", the infinitive.

Thank you very much!

[Sage Pearce-Higgins]

This idiom is just one way of giving the information about public Internet in La Plata. We could use other idioms! I'm guessing that you're not a first-language English speaker; idioms probably are going to be a difficult area for you, because they won't "feel" right or wrong for you. The good news is that there are other ways to solve this problem:
(A) The semicolon (;) means that we need two complete sentences, but the first part isn't a complete sentence.
(B) By putting the verb 'has', the meaning of the first phrase is that 'one of the cities in La Plata'.
(D) This doesn't have a main verb.
(E) Same problem as B