Some reasoning behind the answer would be great, Thank you.

A class Particle has a private field double velocity and public methods double getVelocity() and void setVelocity(double v). It also has a method public void hit(Particle p) { } Which of the following could replace in it to make it compile with no errors? I. double v = getVelocity(); setVelocity(p.getVelocity()); p.setVelocity(v); II. double v = velocity; velocity = p.getVelocity(); p.setVelocity(v); %3D III. double v = velocity; velocity = p.velocity(); p.velocity = v