The Danube is the second longest river in Europe flowing from Germany to the Black Sea passing through ten different countries. It is a major water supply for irrigation, crops and drinking water for millions of people, and is used as a major shipping route and for cultural tourist destination. (A) is correct as it passes through Budapest, Vienna, Bratislava and Belgrade (all capital cities), (C) is correct as there are many tourists travel to the river on cruises, (B) could be correct also, however its main natural resource is water, and its route, so I would not consider it to have "many" natural resources. And (D) would not be correct as the river flows West to East not North to South.
