Concept:The quality that most directly builds moral purity and uprightness in a Muslim.Explanation:In Islam, constant prayers (Salah) restrain a person from sin and immorality.The Quran says prayer prevents indecency and evil, so it purifies the believer’s character.Eid, Quranic studies, and pilgrimage are important, but they are not the daily moral guard that prayer provides.Answer:B. constant prayers