Answer: C - The best choice is "She attended public schools in Montana and"
Generally, commas are used before coordinating clauses such as "and" in sentences with two independent clauses. Periods and semicolons are inappropriate types of punctuation to use with this sentence. Since the clause after "and" cannot stand alone as a sentence, no punctuation is needed before the conjunction. If the second clause was "...and she graduated...." then Choice A would be correct. However, without a subject in the second clause, it cannot stand alone as a complete sentence and is thus not an independent clause. Therefore, the comma is not to be used.
