Question

How could shifts in the physical environment have caused major changes in early civilizations (select 2)
A) Build up of silt could have made Rivers less salty increasing the supply of clean water
B) too much or too little rain May have ruined crops creating food shortages
C) Long term farming could have improved the quality of soil increasing crop yields
D) earthquakes or eruping volcano's may have destroyed communities

Answer 1

The correct options are B AND D.
Agriculture was the major means of survival for men during the early days. Fluctuations in the rainfall during the course of a year may adversely affect the crops grown. If this persists for a long time it will leads to food shortage and famine. 
Earthquake and eruption volcanoes are shift in the physical environment which can easily destroy any community.