He has made another wonderful discovery, _____ I think is of great importance to science.
| A．which | B．what | C．when | D．that |
One solution to this problem now is sustainable development.
| A．discussed | B．discussing |
| C．to be discussed | D．being discussed |
Wind power units are placed ______ there is a lot of wind.
| A．where | B．when | C．which | D．that |
Recently, there a boom in population movements.
| A．is | B．was | C．has been | D．had been |
______developing countries need to do is to stop poverty.
| A．How | B．That | C．Which | D．What |
That's the best way you thought of _______ into dangerous areas.
| A．stopping people to get | B．to stop people getting |
| C．keeping people getting | D．preventing people in getting |