Answer: A. The net force acting on it is zero.
According to Newton’s first law of motion, a body will continue to be in its present state of rest. Also, it can move in a straight line. However, it can stop if it is acted upon by an external force. An object will therefore remain at rest forever unless a net force greater than zero acts upon it. A book placed on a table will remain on that table (state of rest) because the net force acting on that table is equal to zero. Therefore, the only possible thing that can move that book from the position where it is to a new position is a net force greater than zero. This ability for a body to remain at a constant state of rest unless acted upon by an external force is known as inertia.