Groundwater is the water found below the surface of the ground. Water from this source is drawn for various purposes and is replenished by rainwater. Shown here is a graph showing varying groundwater levels in a region, from January '99 to April '00.
During which period was there no change in the rate of rainfall?
(Assume that the usage of water is constant throughout the period shown in the graph.)
A) Mid-July '99 to September '99
B) May '99 to Mid-July '99
C) September '99 to March '00
D) March '00 to April '00
