The answer that has no errors in punctuation or capitalization is option A. "So," asked Vincent, "what do you plan to build?" The rules in using the comma and quotation marks together are correctly applied in this sentence. It is always a rule in interrupted quotations, that commas should be applied inside before the closing quotation mark, and another comma should be applied before the open quotation mark. In addition, the punctuation question mark should also be inside the quotation mark.
