Chọn C.
HOOC-(CH2)4-COOH (X3) + H2N-(CH2)6-NH2 (X5) ® poli(hexametylen ađipamit) + 2nH2O.
NaOOC-(CH2)4-COONa (X1) + H2SO4 ® HOOC-(CH2)4-COOH (X3) + Na2SO4.
CH3OH (X1) + CO ® CH3COOH (X5).
C2H5OOC-(CH2)4-COOH (X) + 2NaOH ® NaOOC-(CH2)4-COONa + C2H5OH (X2) + H2O.
2C2H5OH + HOOC-(CH2)4-COOH ® C2H5OOC-(CH2)4-COOC2H5 (X6) + 2H2O.