Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: The earth's magnetic poles have switched places repeatedly in the past.

A: The earth's magnetic poles have done what repeatedly in the past?
****
Q: The ileocecal valve, a sphincter, is usually in a constricted state, but when motility in the ileum increases, this sphincter relaxes, allowing food residue to enter the first portion of large intestine.

A: The ileocecal valve, a sphincter, is usually in a constricted state, but when motility in the ileum increases, this sphincter relaxes, allowing food residue to enter the first portion of what?
****
Q: Plates are thin , young , and hot causes earthquakes at mid-ocean ridges to be small and shallow.

A:
What causes earthquakes at mid-ocean ridges to be small and shallow?
****