Which of the following is correct order of ligand field strength?

1. A $\mathrm{S}^{2-}<\mathrm{C}_{2} \mathrm{O}_{4}^{2-}<\mathrm{NH}_{3} <$ en $<\mathrm{CO}$ Correct answer
2. B $$\mathrm{CO}<\mathrm{en}<\mathrm{NH}_{3}<\mathrm{C}_{2} \mathrm{O}_{4}^{2}<\mathrm{S}^{2-}$$
3. C $\mathrm{S}^{2-}<\mathrm{NH}_{3}<$ en $<\mathrm{CO}<\mathrm{C}_{2} \mathrm{O}_{4}^{2}$
4. D $$\mathrm{NH}_{3}<\mathrm{en}<\mathrm{CO}<\mathrm{S}^{2-}<\mathrm{C}_{2} \mathrm{O}_{4}^{2}$$