At what level are people considered to be low-income

Can someone me? i need to have this done as soon as possible! i'm putting 20 points on this!

What was the great rift valley formed by

What's a recharge area? a. the part of an aquifer where groundwater meets a lake or stream b. the part of an aquifer where surface water reaches the water table c. the part of an aquifer that's located between two aquicludes d. the part of an aquifer that's located at a lower elevation