Why can't all mixtures be classified as solutions?
question 1 options:
not all mixtures are homogeneous.
not all mixtures are heterogeneous.
not all mixtures have solutes and solvents.
mixtures are made of only one substance.

Answer is: Not all mixtures have solutes and solvents.

Solution is homogeneous mixture composed of two or more substances.  

In aqueous solution, solvent is water and solute (for example salt) is a substance dissolved in water.  

Homogeneous solution of salt and water can be separated with heating (evaporating the water).