Answer : 1. "Liza is regarded as an expert by all of us."
Explanation :

In Active Voice, a sentence emphasizes the subject, performing an action. In Passive Voice, a sentence emphasizes the action or the object of the sentence.
The given sentence is in the active voice and 'We' is the subject and 'Liza' is the object.
When we convert this sentence into passive voice, the subject 'We' of the active voice becomes the object 'us', the object 'Liza' becomes the subject.
The passive format "is + V3 (regarded)" should be used. This is the active and passive voice rule for the present simple tense.