Answer:
Divergent boundaries also form volcanic islands, which occur when the plates move apart to produce gaps that molten lava rises to fill. Current research indicates that complex convection within the Earth's mantle allows material to rise to the base of the lithosphere beneath each divergent plate boundary.
He needs to know if the disorder occurs in the members of family (it would suggest genetic cause of a disease) or in housemates/colleagues from work (it would suggest environmental cause if sick people share the environment)
Because it make it a little more flexable
