I used to meet him occasionally onFifth Avenue.
A.one time
B.in one occasion
C.once in a while
D.none is correct

Biogas can be utilized for electricity production, cooking, space heating, water heating and process heating.
A.generation
B.increase
C.reformation
D.sparing

___________ at the Isthmus of Panama, so animals were able to migrate between North andSouth America.
A.With a land bridge
B.When a land bridge existed
C.A land bridge
D.A land bridge existed

Manufacturers can help conserve mineral and timber supplies ___________.
A.that recycles materials being left over from production processes
B.which recycling materials left over from production processes
C.by recycling materials left over from production processes
D.recycling materials which left over from production processes

Only for a short period of time __________ run at top speed.
A.that a cheetah can
B.can
C.cheetahs
D.do cheetahs

A.punished
B.cooked
C.markedly
D.laughed

_______ (18)
A.into
B.from
C.under
D.to

_______ (17)
A.performance
B.director
C.writer
D.dancer

_______ (13)
A.so
B.come
C.such
D.go

_______ (15)
A.later
B.lately
C.the latter
D.the latest