Why do scientists think earth's core contains iron?

The overall specific gravity of the earth is much higher than the specific gravity of crustal rocks which means the earth is about twice as heavy as the rocks on the surface would suggest. Iron meteorites are thought to have the same composition as the average earth, and the meteorites contain a lot more iron than the Earth's surface rocks. 

Dall of the above all of the choices make sense

Icant awnser the qustion bc u have the planets not listed