The creation of the word enthuse from enthusiasm is an example of back formation. The correct answer is option D. Enthuse is a verb that is a 19th-Century back formation from the word enthusiasm. This word is now commonly used at present and is used as a verb that means "to express enthusiasm".
To show emphasis, the helping verb that would be used to fill the blank in the sentence would be do. I do think I have mastered french pronunciation. Hope this helped :D
