A new technique_________, the yields as a whole increased by 20 percent.
| A．working out |
| B．having worked out |
| C．having been worked out |
| D．to have been worked out |
---Is he here now?---No, I ___ he ___ here by now.
| A．thought, was | B．think, will be | C．think, is | D．thought, had been |
My brother tried ___, but still he couldn't work out this maths problem.
| A．a great deal of | B．a great deal | C．a number of | D．lots of |
He seemed as if he ___ his homework when his mother came in.
| A．did | B．is to be doing | C．were doing | D．be doing |
The poster says that a writer and poet ___ to give us a talk on English next week.
| A．is | B．are | C．be | D．will be |
How this kind of plant can be ____ in a special way is still unknown to us.
| A．kept away | B．kept out | C．kept alive | D．kept off |