The third option "The earliest form of the internet was designed more than thirty years ago, it was intended to be used by the military." does not correct the run-on sentence. By placing a comma, the sentence is still a run on, but it is read with an unnecessary pause. In order to make this correct, a conjunction must be used to connect the sentences (e.g. "and" in option B). I hope this helps you! Have a fantastic day!
