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)