Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: An important function of the circulatory system is transporting oxygen to cells. Answer: circulatory system

Answer: Which system transports oxygens to cells?

Question: Passage: Electromagnetic waves vary in their wavelengths, frequencies, and energy levels. The full range of electromagnetic waves makes up the electromagnetic spectrum. Answer: electromagnetic spectrum

Answer: What do we call the full range of electromagnetic waves?

Question: Passage: Different radioisotopes may vary greatly in their rate of decay. The more unstable their nuclei are, the faster they decay. Answer: unstable

Answer:
Radioisotopes may vary greatly in their rate of decay, decaying faster if their nuclei are more what?