which is correct:

1. the strategy has been proved to be effective.
2. the strategy has been proved effective.
3. the strategy has proved to be effective.
4. the strategy has proved effective.

5. the strategies have been proved to be effective.
6. the strategies have been proved effective.
7. the strategies have proved to be effective.
8. the strategies have proved effective.


Provided you capitalized the first word of each sentence Emotion: sad , all eight would be correct! Emotion: smile
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Thanks. Any differences? Active and passive voices have the same meanings?
The proof is much stronger in 1, 2, 5, and 6. Someone proved that the strategy was effective, although it is expressed in the passive.

In the others, "proved to be" is as weak as "was found to be", "turned out to be", "was seen to be".

The problem was proved to be unsolvable. (Some sort of mathematical proof was probably involved here.)
The problem proved to be more difficult than we thought. (No one proved anything. No one provided any sort of proof. It just turned out, as we discovered (by trying to solve it), that the problem was more difficult than expected.

Got it, thanks a lot.
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