The graduating students are busy _______ material for their reports.
| A．collect | B．to collect | C．collected | D．collecting |
Lack of money led the company to a situation _____ they had to decide whether they should keep on with their production.
| A．when | B．where | C．that | D．which |
. _____ by the advances in technology, many farmers have set up wind farms on their land.
| A．Being encouraged | B．Encouraging |
| C．Encouraged | D．Having encouraged |
_____ the police thought he was the most likely one, they could not arrest him since they had no exact proof about it.
| A．Although | B．As long as | C．If only | D．As soon as |
The wild flowers looked like a soft orange blanket _____ the desert. 
| A．to cover | B．covered | C．cover | D．covering |
30. My parents have promised to come to see me before I _____ for Africa.
| A．have left | B．leave | C．left | D．will leave |