(i) if a1, a2, . am are each countable sets, then the union theorem 1.5.8. a1 u a2 uam is countable. (ii) if a is a countable set for each n e n, then uan is countable.

Cause of he different elevations  hope this ?

1.  culture plays a role in boundary disputes.
2.  female children are encouraged to marry at a young age.
3.  forests are cleared to provide housing.
4.  settlement patterns are influenced by culture.
5.  spanish is spoken in parts of texas.

The second one. this is because the crust is thin, while the mantle is the thickest layer. also, the core is the highest in temperature because of all the pressure from the other layers, so it's solid iron and nickel.