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

Ex Input:
Passage: According to the table, aluminum has an atomic number of 13. Therefore, every aluminum atom has 13 protons in its nucleus. Iron has an atomic number of 26. Therefore, every iron atom has 26 protons in its nucleus. Carbon has an atomic number of 6. Therefore, every carbon atom has 6 protons in its nucleus. Saylor URL: http://www. saylor. org/books. Answer: nucleus

Ex Output:
According to the table, aluminum has an atomic number of 13. therefore, every aluminum atom has 13 protons in its what?

Ex Input:
Passage: The strength of bases is measured on a scale called the pH scale, which ranges from 0 to 14. On this scale, a pH value of 7 indicates a neutral solution, and a pH value greater than 7 indicates a basic solution. The higher the pH value is, the stronger the base. The strongest bases, such as drain cleaner, have a pH value close to 14. Answer: ph scale

Ex Output:
The strength of bases is measured on what scale?

Ex Input:
Passage: Metamorphic rocks form as an existing rock is altered by high temperature or pressure. Answer: metamorphic

Ex Output:
What kind of rocks form as an existing rock is altered by high temperature or pressure?