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

[Q]: Some meteorites are made of iron and nickel and are thought to be very similar to the core of the earth.
[A]: Some meteorites are made of iron and nickel and are thought to be very similar to what part of the earth?

[Q]: Fermat's principle states that light will always take the path of the least amount of time.
[A]: Fermat's principle states that light will always take the path of least amount of?

[Q]: The long, threadlike extensions of the nerve cell help transmit nerve impulses.
[A]:
Which part of the nerve cell helps transmit nerve impulses?