21. Such ____ medical equipment is in ____ danger of breaking down, if not taken good care   

   of.

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

22. Mr. Herre is the one of many experts ____ in our factory.

A. that is           B. that are        C. which is          D. which are

23. --- Do you think we should accept that offer?

   --- Yes, we should, for we ____ such bad luck up till now, and time ____ out.

    A. have had; is running               B. had; is running

    C. have; has been run                 D. are having; runs