As someone who writes books, I'd normally use quotation marks, and the person is obviously talking, so the first one should be correct.
<span>Everyday at twelve o'clock out lunch break, I take a walk around the park.
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Before the test we have studied enough to pass it.
<span>In order to vary the sentence structure, the sentence I would insert in the blank is C. Have you noticed how hard she works? The reason for this is because inserting an interrogative sentence that has a completely different structure and word order than the other two sentences works great in order to introduce some versatility into a paragraph consisting of a couple of sentences. Here, the only sentence that differs is C. which is why you should choose it. Starting three sentences in a row with the same word can be a bit dull and repetitive. </span>