Explain why the inner core remains a solid even though it is very hot.

The inner core is solid because it is made of very dense, or heavy, materials - like iron and nickel. Even though it is very hot, these materials don't "melt" very easily, so they stay solid. Also, pressure due to the weight of the mantle and crust, atoms are forced together as solid. 

Icant awnser the qustion bc u have the planets not listed

The "highest" point is a single point. 
there can't be more than one "highest" point.
it's not possible for every point on a line to be the "highest" one.