21. ______is a good chance that I’ll finish the work tomorrow.

A. It              B. There            C. This              D. That

22. Zhang Jianqi said the mission would be ______ to the country’s future plans to build a space lab and a space station.

A. significance                                B. of great significance

C. of significant                              D. of very significance

23. ________ I sympathize with those who have gone bankrupt£¬ I can’t really do very much to help them out of the difficulties£¬ especially when the US economy has moved into a recession.

A. As long as                    B. As

C. While                           D. Even