**Pushing Force**

Pushing force is a type of force exerted on an object in order to move it away from the person or object applying the force. It is the force that causes an object to move in the direction in which the force is applied. In the context of the given options, the action of kicking best describes the pushing force. Let's discuss the other options to understand why they do not describe pushing force.

**a) Kicking:**

Kicking involves using the foot to strike an object or person. When we kick an object, we exert a force in the direction opposite to our foot's movement. This force pushes the object away from us, making it an example of pushing force. Therefore, option A is the correct answer.

**b) Lifting:**

Lifting involves applying an upward force to raise an object against the force of gravity. When we lift an object, we exert an upward force that counteracts the downward force of gravity. This is not an example of pushing force as the force is directed upwards rather than away from us.

**c) Picking:**

Picking an object typically involves grasping it with our hands and lifting it. Similar to lifting, picking does not involve pushing force. Instead, it involves exerting an upward force to raise the object.

**d) Opening:**

Opening refers to the action of separating the parts of something, such as opening a door or a jar. While opening may require exerting force, it is not necessarily a pushing force. The force applied during the opening action can vary depending on the type of object being opened. For example, opening a door may involve pulling or twisting rather than pushing.

In summary, among the given options, kicking is the action that best describes pushing force. It involves exerting a force in the opposite direction of the movement, causing the object to move away from the person applying the force.