TASK DEFINITION: Given a scientific passage and an answer, generate a question for the given answer.
PROBLEM: Passage: Acidity is measured on a pH scale. Rain that is 5.0 or less on that scale is considered acid rain. Answer: ph scale

SOLUTION: Acidity is measured on what kind of scale?

PROBLEM: Passage: Heat waves have increased in frequency and duration in recent years. The summer 2011 North American heat wave brought record temperatures across the Midwestern and Eastern United States. Many states and localities broke records for temperature and for the most days above 100 o F. Answer: cell membrane

SOLUTION: What are all cells surrounded by?

PROBLEM: Passage: Below the topsoil is the "B" horizon. This is also called the subsoil . Soluble minerals and clays accumulate in the subsoil. Because it has less organic material, this layer is lighter brown in color than topsoil. It also holds more water due to the presence of iron and clay. There is less organic material in this layer. Answer: subsoil

SOLUTION:
Soluble minerals and clays accumulate in what soil layer, allowing it to hold more water?