The correct answer is C.
The Hajj is an annual Islamic pilgrimage to Mecca, Saudi Arabia.
It is the birthplace of Muhammad and the site of Muhammad's first revelation of the Quran, thus it is the holiest city for Muslims and a mandatory religious duty that must be carried at least once during their lifetime.
The Hajj demonstrates the solidarity of Muslims people and their submission to God ( Allah ). As a result of the pilgrimages, Mecca has become one of the most cosmopolitan cities in the world, although no-Muslims are prohibited from entering the city.