Lana balanced an equation so that the result was 2C2H3Br + 5O2 → 4CO2 + 2H2O + 2HBr. Which most likely represents the starting equation?

2C4H3Br + 5O2 → 4CO2 + 2H2O + 2HBr
C2H3Br + 5O2 → 4CO2 + H2O + 2HBr
C4H3Br + O2 → CO2 + H2O + HBr
C2H3Br + O2 → CO2 + H2O + HBr