The angle which an inclined plane makes with the horizontal when a body placed on it is about to move down is known as angle of_______________?

A. coplanar
B. meet at one point ;
C. both A. and B. above
D. all be equal
E. something else

A. balance each other
B. cannot balance each other
C. produce moment of a couple
D. are equivalent
E. none of the above

A. reaction of any smooth surface with which the body is in contact
B. reaction of a rough surface of a body which rolls on it without slipg
C. reaction at a point or an axis, fixed in space, around which a body is con-strained to turn
D. all of the above
E. none of the above