Great changes _______ in this city over the past five years.
| A．took place | B．have taken place | C．were taken place | D．have been taken place |
The students are forbidden，unless they have special passes，________after 11 p.m.
| A．of staying out | B．to stay out | C．staying out | D．stay out |
It's quite obvious that the aging population in China will causeheavy pressure on ________ whole society in the future．
| A．／；the | B．the；／ | C．a；the | D．a：a |
Taobao.com has begun selling tickets online for international flights, ______ to cut the market share of Ctrip.com and other competitors.
| A．to aim | B．having aimed | C．aiming | D．being aimed |
Employers often give jobs to _______ they believe has work experience and a stong sense of duty.
| A．whoever | B．whomever | C．who | D．whom |
Standing on the top of the hill, one would not do anything, but _____ the flowing of the clouds around me.
| A．enjoy | B．enjoying | C．enjoyed | D．to enjoy |