A new theory ______ before it can be put into practice.
A: must be tested
B: be tested
C: can be tested
D: to be tested
A: must be tested
B: be tested
C: can be tested
D: to be tested
举一反三
- Instrument relevance can be easily tested in practice.
- Instrument relevance can be easily tested in practice. A: 正确 B: 错误
- You can’t use the machine because it __________________ (not test) yet. A: has not been tested B: was tested C: has tested
- You can't use the machine because it ___ yet. A: has not tested B: has not been test C: has not been tested
- Sometimes new ideas have to be tested many times before ______ .