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

Input: Consider Input: Passage: For feeding, the insect head contains one pair of lower jaws and two pairs of upper jaws. Insects have also evolved a wide range of specialized mouthparts for eating certain foods. You can see some examples in Figure below . Answer: two pairs

Output: How many pairs of upper jaws do insects have?

Input: Consider Input: 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

Output: Acidity is measured on what kind of scale?

Input: Consider Input: Passage: Empirical formulas can be determined from the percent composition of a compound. In order to determine its molecular formula, it is necessary to know the molar mass of the compound. Chemists use an instrument called a mass spectrometer to determine the molar mass of compounds. In order to go from the empirical formula to the molecular formula, follow these steps:. Answer: molar mass
Output: In order to determine its molecular formula, it is necessary to know what about the compound?