**Net Zero Unbalanced Force:**

When an object experiences a net zero unbalanced force, it means that the sum of all the forces acting on the object is zero. In other words, the forces in all directions cancel each other out, resulting in no overall force acting on the object.

**Constant Velocity:**

If a body experiences a net zero unbalanced force, it will continue moving with a constant velocity. This is because the absence of a net force means there is no acceleration acting on the object. According to Newton's first law of motion, an object in motion will continue to move at a constant velocity unless acted upon by an external force. Therefore, if the object is already in motion and no unbalanced force is acting on it, it will continue moving at the same speed and in the same direction.

**Rest and Unbalanced Force:**

The option 'b' states that the body cannot remain at rest if it experiences a net zero unbalanced force. This is incorrect because an object at rest will remain at rest if the net unbalanced force acting on it is zero. In this case, there is no force to overcome the inertia of the object and set it in motion.

**Acceleration and Unbalanced Force:**

The option 'c' states that the body can be accelerated even if it experiences a net zero unbalanced force. This is also incorrect. Acceleration occurs when there is a net unbalanced force acting on an object. In the absence of a net force, there is no acceleration.

**Conclusion:**

The correct answer to the question is option 'A' - If an object experiences a net zero unbalanced force, it moves with constant velocity. This is because there is no force to change its state of motion.