Mr. Smith is always on time for everything. How ________ it be that he was late for the flight?
| A．can | B．must | C．may | D．need |
29. Studies show that the things that contribute most to a______of happiness cannot be bought．
| A．cause | B．thought | C．suggestion | D．Sense |
28. —Has your sister finished her novel yet?
—I have no idea．She________it last week.
| A．wrote | B．has written | C．was writing | D．had written |
27．To shut your eyes to facts．as many of you do,_______foolish．
| A．is | B．are | C．are | D．Were |
26．There are all sorts of ways that employees can be successful_________obtaining the better office environment.
| A．in | B．On | C．about | D．For |
25. Thirty years ago this month，China's leaders launched an economic revolution.___________the door to free market reforms and foreign trade．
| A．to open | B．opened | C．opening | D．having opened |