We avoid passive sentences with the perfect continuous tenses. In theory, the passive form of your original sentence would be "The bridge has been being repaired..", but in practice we would never say this - it is just too awkward. Instead, we'd find other ways of saying it. If we just wanted to avoid mentioning the government, we'd use the impersonal 'They' and say 'They've been repairing the bridge..'. Or if we wanted to make 'The bridge' the subject, we'd use a noun phrase such as 'The bridge has been under repair for 20 years'.

You did it correctly, good job! But for the past action you could also use “The bridge was being repaired by the government for 20 years.” I hope it helps, :)

I am not sure, what you want to know, but they are both grammatically correct. They do, however, have a slightly different meaning. The first sentence means, that the bridge is repaired /intact -> The process of repairing is over The second sentence indicates that the repairing is still in progress... If you want to make the active sentence passive, you would need the second version, since the repairing doesn't seem to be over yet, even though it has already been 20 years of repairing.... And obviously the first version is NOT in the continuous form Hope this helps

NB The four passive sentences above are correct in themselves, but they are not the passive forms of your original sentence: they have a different meaning. Your original sentence is present perfect continuous, while your passive sentences are present perfect (which means that the repair is now complete) and present continuous (which cannot include the time that the repair has been going on).