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

[Q]: Passage: Wavelength is one way of measuring the size of waves. It is the distance between two corresponding points on adjacent waves, and it is usually measured in meters. How it is measured is a little different for transverse and longitudinal waves. Answer: waves
[A]: What do wavelengths measure the size of?

[Q]: Passage: All the atoms of a given element have the same number of protons in their nucleus, but they may have different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes . Their nuclei are unstable, so they break down, or decay, and emit radiation. Answer: protons
[A]: All the atoms of a given element have the same number of what in their nucleus, though they may have different numbers of neutrons?

[Q]: Passage: Mutations that lead to cancer usually occur in genes that control the cell cycle. These include tumor-suppressor genes and proto-oncogenes. Answer: proto-oncogenes
[A]:
Mutations that lead to cancer usually occur in genes that control the cell cycle. these include tumor-suppressor genes and what?