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

[EX Q]: Passage: Waves are characterized by their ability to constructively and destructively interfere . Light waves which interfere with themselves after interaction with a small aperture or target are said to diffract . Answer: diffract
[EX A]: Light waves which interfere with themselves after interaction with a small aperture or target are said to what?

[EX Q]: Passage: Centrioles are rod-like structures made of short microtubules. Nine groups of three microtubules make up each centriole. Two perpendicular centrioles make up the centrosome . Centrioles are very important in cellular division, where they arrange the mitotic spindles that pull the chromosome apart during mitosis. Answer: centrioles
[EX A]: What are the rod-like structures made of short microtubules that play an important part in cellular division?

[EX Q]: Passage: Ultrasound is sound that has a wave frequency higher than the human ear can detect. It includes all sounds with wave frequencies higher than 20,000 waves per second, or 20,000 hertz (Hz). Answer: ultrasound
[EX A]:
What do you call sound that has a wave frequency higher than the human ear can detect?