Analysis: According to the history of physics and common sense answers, just remember the main contributions of famous physicists. 1932, American physicist Lawrence invented the cyclotron, which skillfully used the motion characteristics of charged particles in the magnetic field to solve the problem of particle acceleration. So C. Comments: This question examines the history of physics and is a common sense question. Strengthening the memory of major discoveries, inventions and famous theories in physics is also one of the examination contents.