The Rest Energy of an Electron and Its Antiparticle,a Positron,is

Multiple Choice

The rest energy of an electron and its antiparticle,a positron,is 0.511 MeV.In order to produce an electron-positron pair,a gamma ray must have an energy larger than 1.022 MeV because of

A) time dilation.
B) length contraction.
C) the equivalence of mass and energy.
D) the principle of relativity.
E) none of the above.