21. The new building will be built _________ was a wasteland 30 years ago.

A. in what          B. where              C. in which          D. there

22. --- Do you still remember when we went to Nanjing?

--- I can’t remember now but _________ sometime last summer?

A. might it be                            B. could it be

C. could it have been                       D. should it have been

23.  Thanks for your kind help! We would have ____ lost the game!

A. therefore    B. or    C. otherwise    D. then