the presence of a fluid mantle the presence of Van Allen belts the presence of gravitational force the presence of water in three states
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Earth's core consists primarily of iron. Which observation about another planet would provide some evidence that the planet has an iron core?
Possibilities:
- the presence of a fluid mantle
- the presence of Van Allen belts
- the presence of gravitational force
- the presence of water in three states

the presence of Van Allen belts