11. The teachers at Edinburgh College encourage students to _____________ with others, experiment with arts and find their own ideas.
A. help B. improve C. involve D. collaborate
12. University _____________ in Viet Nam can decide their own criteria for enrolling international students.
A. principals B. rectors C. headmaster D. managers
13. Humans do harm to the environment by _____________ atmospheric carbon dioxide concentration by a third since the Industrial Revolution began.
A. increasing B. having increased
C. having been increased D. being increased
14. _____________ the desalination plant, the company could offer an effective solution to the problem of water scarcity.
A. To build B. Having built C. Being built D. Having been built
15. The public praised the local farmers for _____________ millions of trees on the surrounding hills.
A. plant B. being planted C. being planting D. having planted
