💡 Detailed Explanation
The man is highly praising Yamada-san, attributing the project's success entirely to them. The most natural and appropriate response in Japanese business culture is to show modesty by saying 'No, no,' and attributing the success to the entire team, not just oneself. 'Hitoeni' means 'entirely' or 'solely.' Option A is too arrogant. Option B misunderstands 'okage' (thanks to) as 'sei' (fault).