The purification and removal of bacteria, solid materials and other impurities from used water is classified as

The higher level of floods and droughts are led by

A. sand storms

B. lower precipitation

C. higher precipitation

D. none of the above

The careful management of water catchment areas results in

A. more desertification

B. more deforestation

C. less waste of water

D. more waste of water

The percentage of Earth surface which is covered by oceans and seas is

A. 50%

B. 65%

C. 85%

D. 97%

The percentage of surface of Earth which is covered by water is

A. 70%

B. 85%

C. 90%

D. 60%

The methods used for desalination are

A. membrane filtration

B. distillation

C. cloud seeding

D. both a and b