21. – What about _____ conference you attended last week?
   -- To tell the truth, it was boring, you know, _____ conference like that.
    A. the; a                    B. the; /                        C. a; the                       D. the; the

22. I would really appreciate _____if you would like to teach me how to monitor the robots.

A. that                         B. this                          C. it                            D. you

23. You know, Bob is a little slow _____ understanding. So I have to be patient _____ him.

       A. in; with                    B. on; with                   C. in; to                       D. at; for