To answer this question, the user needs to know how to express "no mention" or "no problem" in Japanese.
Out of the given options:
A. Ohayou gozaimasu - This phrase means "good morning."
B. Arigatou gozaimasu - This phrase means "thank you very much."
C. Onegaishimasu - This phrase means "please" or "I humbly request."
D. Dou itashimashite - This phrase means "you're welcome" or "don't mention it."
Therefore, the correct answer is D. Dou itashimashite is the appropriate phrase to use to indicate "no mention" or "no problem" in Japanese.