11. Which of the following statement is correct?
A. The algebraic sum of the forces, constituting the couple is zero.
B. The algebraic sum of the forces, constituting the couple, about any point is the same.
C. A couple cannot be balanced by a single force but can be balanced only by a couple of opposite sense.
D. all of the above
12. The velocity ratio of a differential wheel and axle with D as the diameter of effort wheel and d1, and d2 as the diameters of larger and smaller axles respectively, is
