A:用铂电极电解氯化镁溶液:Cl-+2H2OCl2↑+H2↑+2OH-
B:NaHSO4溶液中滴入Ba(OH)2溶液至中性:H++SO42-+Ba2+十OH-===BaSO4↓+H2O
C:在H2O2中加入酸性KMnO4溶液:2MnO4-+5H2O2+6H+====2Mn2+ +5O2↑+8H2O
D:溴乙烷与6mol/L氢氧化钠水溶液共热:C2H5Br +OH-CH2=CH2↑+Br-+H2O
如图,已知AB∥CD∥EF,AD:AF=3:5,BE=10,那么BC的长等于____.