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

[EX Q]: Passage: The problem doesn't stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. Answer: months
[EX A]: In places where crops grow only during part of the year, the land may be bare for a few?

[EX Q]: Passage: Benzoic acid crystals in polarized light are pictured above. Benzoic acid is widely used as a food preservative, either as the carboxylic acid or as the sodium benzoate salt. This compound is most effective when added to acidic foods such as fruit juices and soft drinks. The major industrial source of benzoic acid is the partial oxidation of toluene with oxygen. The process is inexpensive and environmentally benign. Answer: benzoic acid
[EX A]: What type of acid is often used as a preservative for acidic foods such as fruit juices?

[EX Q]: Passage: The sun and other stars produce light because they are so hot. They glow with light due to their extremely high temperatures. This way of producing light is called incandescence . Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes. Producing light without heat is called luminescence . Objects that produce light by luminescence are said to be luminous. Luminescence, in turn, can occur in different ways:. Answer: luminescence
[EX A]:
Producing light without heat is called what?