16.Contracts must be renewed one week ____ their expiration.
A.on
B.against
C.the moment of
D.before
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17.As mentioned ____ my letter of August 6, the shoes were not satisfactory.
A.on
B.at
C.for
D.in
18.The goods will be shipped ____ October 1.
A.in
B.to
C.on
D.with
19.We will write ____ you as soon as we are able to supply these goods again.
A.until
B./
C.while
D.as
20.Please try your best to ship our order ____ that steamer.
A.by
B. for
C.in
D.with
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