Answer:
The sentence that best integrates the quote into the text is <em>C. Dr. Glass asserts, "there is absolutely no proof that breaking a mirror can cause bad luck."</em>
Explanation:
The correct way to introduce a quotation when the introductory phrase is not a complete sentence -like <em>Dr. Glass asserts</em>- is to separate it from the quotation with a comma.
Moreover, in America, commas and periods should always go inside the quotation marks -like in "<em>...bad luck</em>."
Therefore, sentence C is the one that best integrates the quote into the text.