How does over-irrigation damaging to soil?
a. it reduces the amount of organic material in soil..
b. it results in the accumulation of salt near the soil surface..
c. it increases the acidity of soil..
d. it removes water from the water table.

The correct answer is A. It reduces the amount of organic material in soil. 

Over-irrigation can cause the oxygen levels in the soil to decrease. It doesn't result in the accumulation of salt near the soil surface, it doesn't increase the acidity of soil, and it doesn't remove water from the water table. 

Its led to migrationits led to death 

The answer to the first one is barometer.