I believe the answer is Planet Nine.
Answer:
The solute is powdered drink mix
Explanation:
The solute is powdered drink mix is solute because solute is any substance that dissolves in a solvent while solvent is the substance that dissolve solute or the dissolving medium. When solute dissolve in solvent it is called solution.
Solution is an homogeneous mixture of substance which comprises of solute that dissolve in solvent.
I believe the cerebrum is the largest part of the brain, so the answer should be C.