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)

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

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