What inference does Elie make about Rabbi's Eliahou's son when the rabbi is searching for him?

a
The son intentionally ran ahead during the march and left his father behind.
b
The son is dead, though Elie does not tell this to the rabbi.
c
Though unlikely, the son might still be alive, giving the rabbi hope to live.
d
The son fell behind because he no longer had strength to run with his father.