Which example shows correctly punctuated direct dialogue?

The correctly punctuated direct dialogue is found in the response that includes quotation marks around the spoken words. This format indicates that the exact words of the speaker are being presented. In this case, "I plan on majoring in aeronautical engineering" is a complete thought expressed by the speaker, and using quotation marks properly denotes this as a direct quote.

Additionally, the comma before the opening quotation mark is crucial because it separates the speaker's attribution from what is being said. This punctuation structure is in accordance with standard English grammar rules for direct quotations, which require both quotation marks for the spoken words and a comma to introduce the quote.

The use of capital letters and quotation marks in this instance correctly follows the conventions of speech in written form. Overall, the proper implementation of these elements in the selected response ensures clarity and adherence to grammatical guidelines, making it the best choice for correctly punctuated direct dialogue.