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15. The electronic computer _____ these calculations. 1) just performed 2) had just performed 3) were just performing 4) has just performed 16. The controller _____ the disk drive at the present time. 1) run 2) has run 3) is running 4) runs 17. The first electronic computer _____ 30 tons. 1) weighed 2) will weigh 3) has weighed 4) had weighed 18. They _____ several attempts recently to do this hard job. 1) make 2) made 3) are making 4) have made 19. They usually _____ their European meeting in Paris. 1) are holding 2) hold 3) holds 4) have held 20. She _____ in Rome at the moment. 1) works 2) worked 3) is working 4) has worked