(a)Determine all subfields of .(b)Prove that .

Attempt:

For the first part I think . So, I know about the "Subfield Test", but how would I find the possible subfields to be tested? Or is there a simpler way of dealing with this problem?

For the second part to show they're not isomorphic do I just need to show there is not a one to one correspondance? I think has complex numbers whereas the other one does not...