How do tributaries increase the economic benefits of rivers

Tributaries increase the economic benefits of rivers because they provide more opportunities for states to trade, develop agriculture, and to develop industries from waterways. Also tributaries help to increase the fertility of agricultural lands which can also support economic development. Tributaries of rivers can also be used to power dams to create electricity supporting economic growth. 

Answer feldspar,quartz,mica and amphibole;

Answer after wwii, communist countries in eastern europe formed the warsaw pack, a military alliance, and comecon, an economic alliance;