What is the smallest unit ever used in the census geography hierarchy?

Which factors add to the greenhouse effect and are caused by human activities?

Exactly what kind of weather conditions would a cold front produce?

Which statements about wells are true? check all that apply. a) wells bring groundwater from the unsaturated zone to the surface of the water. b) wells need to be drilled below the water table. c) if water is pumped from a well too quicky, the well may run dry. d) water from wells is generally not safe to drink. e) water gushes from artesian wells due to pressure.