Answer:
I think the answer would be option d.
hope it helps.
<h2><u>Answer</u> :</h2>
The most appropriate option is :

Since, they are the most abundant elements found in Earth's Crust.

Correct me if I'm wrong, anyone who is more informed on this than I am, but wouldn't it be because of the magnetic fields and whatnot? The longer I think on it, the more I feel like I'm wrong, so don't take my word for it 100%