This used piston had been tested and approved as a spare part by the （） during last annual repair.
举一反三
- If a better material______, the strength of the part would have been in- creased. A: had been used B: had been using C: being used D: using
- I had no idea of the machine _______ already. A: to test B: having been tested C: testing D: having tested
- He had been in Shanghai since last Friday.
- Ron and Ben had never been to this part of England before.
- He______killed last night if he had taken part in the surprise attack on the night.