Question

where might a spring form?
× between the saturated and unsaturated zones
○ at the bottom of a deep valley
○ on a mountaintop at the origin of a stream
○ on the surface of a fast-moving aquifer

Explanation:

To determine where a spring forms, we analyze each option:

• "Between the saturated and unsaturated zones" is incorrect as the water table (boundary between these zones) when intersecting the surface can form a spring, but the option's phrasing is misleading.
• "At the bottom of a deep valley": Springs often form where the water table meets the surface, and valleys can have this intersection due to topography, allowing groundwater to emerge.
• "On a mountaintop at the origin of a stream": Mountaintops are typically above the water table, so streams there are from precipitation/runoff, not springs.
• "On the surface of a fast - moving aquifer": Aquifers are underground; springs form at the surface where groundwater exits, not on the aquifer's surface.

So the correct option is the one about the bottom of a deep valley.

Answer:

at the bottom of a deep valley