A Photon Hitting an Electron (Mass $m$ ) at Rest Can Create an Electron-Antielectron Pair in Addition

Multiple Choice

A photon hitting an electron (mass $m$ ) at rest can create an electron-antielectron pair in addition to the original electron. Assume that the two electrons and the positron move away from the collision at rest with respect to each other afterward. What was the photon's initial energy?

A) Zero
B) $m$
C) $2 m$
D) $3 m$
E) $4 m$