Friction force for dry surfaces. Friction force is________________?

Pick up wrong statement?
A. proportional to normal load between the surfaces
B. dependent on the materials of contact surface
C. proportional to velocity of sliding
D. independent of the area of contact surfaces
E. none of the above is wrong statement

Which is the correct statement about law of polygon of forces ?

A. if any number of forces acting at a point can be represented by the sides
of a polygon taken in order, then the forces are in equilibrium
B. if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon, then the forces are in equilibrium
C. if a polygon representing forces acting at a point is closed then forces are in equilibrium
D. if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon taken in order, then the forces are in equilibrium
E. none of the above.

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