The research has been conducted sincerely by them for ten years. (Active)

• ক They have been conducting the research sincerely for ten years. ✅ সঠিক উত্তর
• খ They have conducted the research sincerely for ten years.
• গ They had been conducting the research sincerely for ten years.
• ঘ They had conducting the research sincerely for ten years.