Which mixtures act as buffer solutions?

I.     ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ ethanoic acid and ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ sodium ethanoate

II.     ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ ethanoic acid and ${\text{50 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ sodium hydroxide

III.     ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.1 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ ethanoic acid and ${\text{100 c}}{{\text{m}}^{\text{3}}}{\text{ 0.5 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ sodium hydroxide

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A