21£®Although their new factory building is still under          construction, we have already placed         order for 200 pairs of shoes.

       A. the ; an                  B. a; an                      C. /; /                         D. / ; an

22. Receiving a report that the place crashed,          the government took measures.

       A. at no time                                                 B. in no time

       C. at a time                                                    D. of all time

23. The H1N1 virus will spread much faster       people continue to travel as usual.

       A. if                          B. unless                    C. until                      D. in case