The necessary condition of equilibrium of a body is: A. Algebraic sum of horizontal components of all the forces must be zero B. Algebraic sum of vertical components of all the forces must be zero C. Algebraic sum of the moments of the forces about a point must be zero D. All (A), (B) and (C)

The correct answer is D. All (A), (B) and (C).

The necessary condition of equilibrium of a body is that the algebraic sum of the horizontal components of all the forces must be zero, the algebraic sum of the vertical components of all the forces must be zero, and the algebraic sum of the moments of the forces about a point must be zero.

The first condition ensures that the body does not move in the horizontal direction. The second condition ensures that the body does not move in the vertical direction. The third condition ensures that the body does not rotate about any point.

If any of these conditions is not met, the body will not be in equilibrium and will start to move.