If computers ______, many problems on space flight could not have been solved.
A: had not been invented
B: are not invented
C: were not invented
D: have not invented
A: had not been invented
B: are not invented
C: were not invented
D: have not invented
举一反三
- Had electronic computers not been invented, many problems of space flight ______.
- If the personal computer had not been invented, will the information age have arrivied by other means? A: 正确 B: 错误
- 57. James watt ____ the steam engine. A: was inventing B: invented C: had invented D: has invented
- The scientist and engineer ____ (have) invented a new machine. A: are B: was C: has D: were
- James Watt （）the steam engine in 1796. A: discovered B: had discovered C: invented D: had invented