Answer:
1. The hotel will be redecorated by a famous designer.
2. Some trees have been planted by the gardener.
3. Penicillin was discovered by Fleming.
4. Italian is spoken in Italy.
5. Let it be done.
6. By whom was the food being cooked? / The food was being cooked by whom? / Whom was the food being cooked by?
7. Are the rules obeyed by her?
8. Nice songs are sung by Usman.
9. That fence is being repaired by someone.
10. Why has a new car been purchased by them?
Step-by-step explanation:
In general, to form the passive voice of a sentence, we identify the direct object of the verb in the active voice and transform it into the subject. The verb tense should be maintained, but the auxiliary "be" must be introduced. And what was the subject in the active voice becomes the agent of the passive voice, preceded by the preposition "by".
Example: The man cut down the tree. → The tree was cut down by the man.
One detail to be noticed is that the subject "they", when referring to people in general, with no one specific in mind, should be omitted when transformed into the agent. That is what happens in number 4.
Also, imperative sentences in the passive voice employ "let", as can be seen in number 5.