— Is Jack on duty today?
— It ________ be him. It's his turn tomorrow.
| A．mustn't | B．won't | C．can't | D．needn't |
. _____ 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 |
It was the principles I learned from my reading _____ enabled me to get bigger and better jobs.
| A．that | B．which | C．what | D．who |