To answer this question, you need to understand the Japanese phrase for "I understand".
Option A) Wakarimasen - This option is incorrect because "Wakarimasen" means "I don't understand" in Japanese.
Option B) Sumimasen - This option is incorrect because "Sumimasen" means "excuse me" or "I'm sorry" in Japanese, and it is not the phrase for "I understand".
Option C) Ryoukai shimashita - This option is correct because "Ryoukai shimashita" means "I understand" in Japanese. It is a polite way to express understanding or agreement.
Option D) Onegaishimasu - This option is incorrect because "Onegaishimasu" means "please" or "I request" in Japanese, and it is not the phrase for "I understand".
The correct answer is C) Ryoukai shimashita. This option is correct because it accurately translates to "I understand" in Japanese, specifically in a polite form.