Geographers use all of the following measures to determine population trends EXCEPT

the sex ratio.
the natural birthrate.
the crude death rate.
the dependency ratio.
the natural increase rate.

Renaldo and nasreen build an electromagnet by wrapping a wire around a nail and connecting the wire to both terminals of a battery. when they test the electromagnet, it can pick up 6 paper clips. their teacher wants all groups to pick up at least 10 paper clips. what could renaldo and nasreen do to increase the number of paper clips their electromagnet picks up?