A.CnH2n (n ≥ 3).
B.CnH2n-2 (n ≥ 2).
C.CnH2n+2 (n ≥ 1).
D.CnH2n (n ≥ 2).

A.Al3+, Cr3+.
B.Fe2+, Fe3+.
C.Ca2+, Mg2+.
D.Na+, K+.

A.saccarozơ.
B.glucozơ.
C.xenlulozơ.
D.tinh bột.

A.Nilon-6,6.
B.Amilopectin.
C.Xenlulozơ trinitrat.
D.Poli(vinyl clorua).

A.K.
B.Ca.
C.Ag.
D.Fe.

A.CnH2nO2.
B.CnH2n+2O2.
C.CnH2n-2O.
D.CnH2n-4O2.

A.HCOOC6H5; CH3COOC6H5.
B.HCOOC2H5; CH3COOC2H5.
C.HCOOC2H5; CH3COOC6H5.
D.HCOOCH3; HCOOC6H5.

A.was built
B.built
C.build
D.was building

A.The more difficult
B.The most difficult
C.Most difficult
D.Difficult

A.The more difficult
B.The most difficult
C.Most difficult
D.Difficult