Here are the sentences converted from active voice to passive voice:

1) All the details of this area were not told to me (by them).
2) Many postcards have just been sent to this friend by Betty.
3) A playwright is called by people.
4) These films were made from Shakespeare's lines.
5) Various kinds of newspapers are put on the table by him.
6) The stream engine was invented by James Watt.
7) Cars are not made here.
8) English is spoken all over the world.
9) A new hotel is being built at the moment.
10) More pollution is being produced by the factory.
11) Much is told to us about human nature by this film.
12) These plays were written by Shakespeare. (unchanged)
13) Iron cages were kept for the performing animals.
14) A bunch of flowers was given to her by someone.
15) Lions are fed at 3 p.m. every day by the keepers.
16) This pudding can be cooked in its tin. (unchanged)
17) This cheque has not been signed by anyone.
18) She was asked about her new job.
19) He was made to study hard for his exams by his parents.
20) It is believed that he is intelligent.

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