The correct choice is 'Additionally,' because it is the standard way to punctuate a sentence with a transitional word, according to English conventions. The correct answer is option C.
The question asks which choice completes the text following Standard English conventions related to punctuation, particularly when using the word 'Additionally'. This word often introduces an additional point or item, and in formal writing, it is typically followed by a comma.
Therefore, Choice C, 'Additionally,' is the correct choice because it provides proper punctuation with a comma following the transitional phrase, adhering to the conventional use of commas with transitional words and phrases.
This adheres to the editing focus of using commas correctly as discussed in the referenced chapter.