Particle Physics help please

C is the answer, but why? Why not B? Is it because B causes the particle's speed to gradually increase, but the question asks for which option causes the speed to change. I think that option C causes the particle's to accelerate then decelerate then accelerate etc between the dees, causing a change in speed, as asked by the question. So C must be the answer. Am I right in my thinking?

Multiple choice offers seemingly plausible answers and often it is as much a process of logical elimination as it is thinking about the basics that will lead to the correct answer.

a) Incorrect. the magnetic field constrains the possible trajectories and not the speed.

d) Incorrect. the same as for a)

b) Incorrect. The voltage supply is oscillating? Says nothing about what the voltage suppy is connected to. The reader is left to make assumptions about what the voltage supply is doing. i.e. the voltage supply may be connected between one of the Dees and not the other. First rule of science is never make assumptions.

c) Correct. The potential between the 'Dees' produces an electric field. Any charged particle within that field will experience a force and therefore will be accelerated according to Newtons laws.

Change of speed is acceleration.

Therefore c0 is the only logical and correct statement.