Studies done at the time showed such a vehicle was technically feasible, was fairly easy to manufacture and had commercial .
举一反三
- It was the first time ____ we had done the experiment.
- The work_______by the time you get there. A: has been done B: had been done C: will have been done D: will be done
- What ______ Jim ________ by the time he was seven？ A: did, do B: had, done C: have, done
- With a lot of work ______, he had no time to talk with us. A: to be done B: to do C: doing D: done
- The millions of calculations involved, ____by hand, would have lost all practical value by the time they were finished. A: had they been done B: they had been done C: having been done D: they were done