The correct option is A.
Multiple trial of an experiment normally improve the reliability of the experiment. Repeating an experiment several time using the same procedure usually increase the accuracy of the data obtained. The average of these data can then be calculated to obtain as near accurate result as possible.
Four human impacts on the lithosphere brought on through agriculture are: 1. Increased salinity of the surrounding environment due to pesticide and fertilizer use. 2. Increased soil erosion due to the destruction of the native, protective canopy. 3. Decreased soil productivity due to the overuse of land. 4. Increased pollutants in the groundwater table due to chemical use and/or lower levels of the water table to irrigation and then runoff or evaporation.