A subatomic particle $\backslash (\backslash$mathbf$\{$X$\}\backslash )$ spontaneously decays into two particles, $\backslash (\backslash$mathbf$\{$A$\}\backslash )$ and $\backslash (\backslash$mathbf$\{$B$\}\backslash ),$ each of rest energy $\backslash (1\mathrm{.}40\backslash$times $10^\{2\}\backslash$mathrm$\{$MeV$\}\backslash ).$ The particles fly off in opposite directions, each with speed $0\mathrm{.}827$ c relative to an inertial reference frame $5.$

Which one of the following statements concerning particle $\backslash (\backslash$mathbf$\{$X$\}\backslash )$ is true?Momentum conservation requires that it was moving in frame $\backslash ($ S $\backslash ).$Momentum conservation requires that it must have been at rest in frame $\backslash ($ S $\backslash ).$There is not enough information to determine its state of motion at the time of the decay.Energy conservation requires that its total energy was $280$ MeV in frame $5.$Energy conservation requires that it must have been at rest in frame $\backslash ($ S $\backslash ).$