Given a scientific passage and an answer, generate a question for the given answer.

Input: Consider Input: Passage: Abrasion is another type of mechanical weathering. With abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a slope. Moving water causes abrasion it moves rocks so that they bump against one another ( Figure below ). Strong winds cause abrasion by blasting sand against rock surfaces. Finally, the ice in glaciers cause abrasion. Pieces of rock embedded in ice at the bottom of a glacier scrape against the rock below. If you have ever collected beach glass or pebbles from a stream, you have witnessed the work of abrasion. Answer: mechanical

Output: What kind of weathering is abrasion?

Input: Consider Input: Passage: Hydraulic car lifts also use fluid to transmit pressure and increase force. The lifts are used to raise cars, which are very heavy, so mechanics can work on them from underneath. Controls in airplanes use fluids to transmit pressure and increase force so a flick of a switch can raise or lower heavy landing gear. To see animations of hydraulic systems such as these, go to URLs:. Answer: hydraulic systems

Output: What kind of systems use fluid to transmit pressure and increase force?

Input: Consider Input: Passage: An aquifer is an underground layer of rock that is saturated with groundwater. One of the biggest aquifers in the world is the Ogallala aquifer in the American Midwest. Answer: groundwater
Output: An aquifer is an underground layer of rock that is saturated with what?