The correct option is A Red fort
If the tourist visits Lotus Temple, he must also visit Qutub Minar (since Qutub Minar → Lotus Temple, Lotus Temple ← Qutub Minar). He also visits India Gate. Thus, we know four of the monuments on her route as Qutub Minar, India Gate, Taj Mahal and Lotus Temple. We have to fit in one more monument. If the tourist visits Red Fort, he will also visit Jantar Mantar and Humayun' tomb, and there is no place for those monuments on the itinerary. Therefore, Red fort definitely cannot be one of the remaining 3 monuments.