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: You can't go to the mantle but small pieces of the mantle can come to you. Kimberlite forms deep in the mantle and is erupted violently into the crust. Kimberlite can contain diamonds. Most kimberlites reached the surface much earlier in Earth history. Answer: crust
[A]: What is the upper most level of earth's layers called?

[Q]: Passage: In self-pollination , the egg is fertilized by the pollen of the same flower. Answer: self pollination
[A]:
What is the process by which the egg is fertilized by the pollen of the same flower?