💡 Detailed Explanation
Translation: Mr. Tanaka is talking with Mr. Yamada on the phone.
- Grammatical point: Companion / Mutual action particle と (to - with).
- Explanation: The particle 'と' represents the companion or partner with whom you perform a mutual action (話す - talk, 会う - meet, 結婚する - marry, etc.). '山田さんと話す' means 'talk with Mr. Yamada'.
- Why other choices are incorrect:
- に (ni): Can be used for one-way direction (e.g. 山田さんに電話をかける - make a phone call to Mr. Yamada), but for a reciprocal conversation ('talking with'), 'と' is the most natural fit.
- を (o): Yamada-san is not a direct object of the verb 話す.
- で (de): Represents location or means (電話で is already used for 'by phone').