Final answer:
A magnetic field cannot change the kinetic energy of a charged particle because the force it exerts is perpendicular to the particle's velocity, only altering its direction while the speed remains constant.
Step-by-step explanation:
A magnetic field cannot change the kinetic energy of a charged particle. This is because the magnetic force exerted by the field is always perpendicular to the velocity of the charged particle, which means it can only alter the direction of the particle's movement and not its speed. According to physics principles, when the direction of a particle changes, but its speed remains constant, the particle is undergoing uniform circular motion. For example, when a charged particle like an electron moves perpendicular to a uniform magnetic field (B-field), the magnetic force acting on it provides the necessary centripetal force (Fc = mv² / r), while the kinetic energy and speed stay the same.
The response to the question asked by the student, therefore, would be 'D. change the kinetic energy of a charged particle', reflecting that a charged particle's kinetic energy is not affected by the magnetic field.