21. £Û2012¸£ÖÝÄ£Äâ£Ý____successful launch of Tiangong-1 on September 29th marked ______ significant step in our country’s plan to build a space station£®

A. The; a        B£®/; a                  C£®A; the              D£®/; the

22. You have to study harder, ____you will fall behind others.

A. or                     B. but                   C. so                     D. and