39. 下列混合溶液，何者為緩衝溶液？
(A)0.1 M HCl 10 mL＋0.1 M CH3COONa 15 mL
(B)0.1 M NaOH 20 mL＋0.1 M CH3COOH 10 mL
(C)0.1 M NaOH 15 mL＋0.1 M CH3COOH 20 mL
(D)0.1 M NaOH 20 mL＋0.1 M HNO3 15 mL
(E) 0.1 M CH3COOH 10 mL＋0.1 M CH3COONa 15 mL