A run-on sentence is a sentence having two independent clauses with improper punctuation and without conjunctions. The correct answer is option b. It is difficult to understand a run-on sentence because you cannot identify where to pause or stop and that the sentence does not have conjunctions which would help in the transition of clauses.
A key concept is an attack that took place. It is developed by providing further explanation of the US Pacific Fleet casualties and the all the warships damaged. and sunk.
A semicolons NEVER should be used to try to create a "pause" longer than that achieved by a comma. If you can use a period correctly, then you can use a semicolon correctly. A semicolon is used just like a period, but it is used to separate two complete sentences when the sentences are closely related in meaning.
The answer is A. However. Hope this helps. :)