Answer:
Option 3 and 6
Explanation:
If the particle is under the action of only one external force, both its kinetic energy and the velocity must vary.
When the particle is exerted by an external force, then this external force tends to accelerate the particle.
When the particle accelerates, its velocity must vary for that acceleration to occur.
When the velocity of the particle changes then its Kinetic energy must vary with the velocity of the particle.