Question

1) Do not distrub him. He ... an experiment (make, is making, makes) 2) When ... the radio invented? (did, is, was) 3) Vacuum tubes ... according to the number of electrodes (is classified, are classified, classified) 4) Great success ... is space research (have been achieved, has been achieved, has achieved) 5) Students usually ... exams at the end of the term (are having, has, have) 6) When I came to them yesterday, they ... a transistor (were constructing, constructed, construct) 7) She ... already ... her work (finished, has finished, have finished) 8) Lectures ... by highly qualified teachers (is delivered, are delivered, are delivering) 9) George ... the university last year (has entered, enters, entered) 10) The problem ... by the professors in a month (investigated, will investigate, will be investigated)

Answer 1

1. is making

2. was

3. are classified

4. has been achieved

5. have

6. were constructing

7. has finished

8. are delivered

9. entered

10. will be investigated

Answer 2

1. is making

2. was

3.are classified

4.have been achieved

5.have

6.were constructing

7.has finished

8.are delivering

9.has entered

10.invastegated

Answer 3

1. Do not disturb him. He is making an experiment.

2. When was the radio invented?

3. Vacuum tubes are classified according to the number of electrodes.

4. Great success has been achieved in space research.

5. Students usually have exams at the end of the term.

6. When I came to them yesterday, they were constructing a transistor.

7. She has already finished her work.

8. Lectures are delivered by highly qualified teachers.

9. George entered the university last year.

10. The problem will be investigated by the professors in a month.