Which pairs of solvents would make good extraction systems?

The use of piers and beams to build a strong foundation for a house.

Sorry i dont understand the question can you rephase it?

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).