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

A.does he
B.isn't he
C.was he
D.didn't he

A.After you had come next time
B.After you come next time
C.When you come next time
D.When you came next time

A.To perform
B.Be performed
C.Performed
D.Having performed

A.although
B.in spite of
C.because
D.because of