12. (1 pt each) For systems C, D, and E, explain what element(s) are unnecessary and why. 13. (1 pt each) Redraw each system from part 2 as a minimal equivalent mechanical system, removing the unnecessary elements. 2 2. (20 Points) Consider the mass-spring-damper system below. The walls are stationary. Elements 1, 3 and 6 are springs, 2 and 4 are masses, and 5 and I" are dampers. Each nonmass element is governed by a linear constitutiye law