Which pair of terms applies to changes such as depletion of underground aquifers and water logging of irrigated soils? 

A)  natural and gradual 
B)  human caused and catastrophic 
C)  human caused and gradual 
D)  natural and catastrophic

Depletion of underground aquifers and water logging of irrigated soils are both examples of human-caused changes that occur over a gradual period of time, making option C the best choice. Option A (natural and gradual) does not apply as these changes are primarily caused by human activities like excessive groundwater pumping and irrigation. Option B (human caused and catastrophic) does not apply as these changes do not typically result in sudden or disastrous events. Option D (natural and catastrophic) does not apply as these changes are not primarily caused by natural forces.