Three forces which act on a rigid body to keep it in equilibrium. The forces must be coplanar and

ANS:A - concurrent

Concurrent forces refer to forces that share a common point of intersection. In other words, they all meet at a single point. This point is where the lines of action of the forces intersect. When forces are concurrent, it means that their effects on the object they're acting upon can be analyzed more easily because their combined influence is concentrated at this point of intersection. The equilibrium of a rigid body under concurrent forces can be analyzed using principles of statics, such as the equilibrium equations. In practical terms, if you have multiple forces acting on an object and they are concurrent, you can simplify your analysis by considering the net effect of these forces at the point of intersection. This simplification is particularly useful in solving engineering problems and understanding the balance of forces in various structures and systems.