pH梯度萃取法分离黄酮苷元类,加碱液萃取的顺序应是
A A:NaHCO<sub>3</sub>→NaOH→Na<sub>2</sub>CO<sub>3</sub> B
B:NaHCO<sub>3</sub>→Na<sub>2</sub>CO<sub>3</sub>→NaOH C
C:NaOH→NaHCO<sub>3</sub>→Na<sub>2</sub>CO<sub>3</sub> D
D:NaOH→Na<sub>2</sub>CO<sub>3</sub>→NaHCO<sub>3</sub> E
E:Na<sub>2</sub>CO<sub>3</sub>→NaHCO<sub>3</sub>→NaOH