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

[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 surface seismic waves do the most damage because they only travel along the surface of the ground. Answer: surface
[EX A]: What type of seismic waves do the most damage?

[EX Q]: Passage: Water is a polar compound, so its molecules are attracted to each other and form hydrogen bonds. Answer: hydrogen
[EX A]:
Water is a polar compound, so its molecules are attracted to each other and form what kind of bonds?