Thank you very much. The sentences you checked are part of an exercise in which students are asked to put the verbs (from the active) into the passive voice. Do you think they are OK or shall I change sentence number 5?
1) He's going to do the washing-up after lunch.
The washing-up is going to be done after lunch.
2) Peter is going to book a seat for tomorrow's concert. A seat for tomorrow's concert is going to be booked by Peter.
3) They were renovating the flat when I was there last week. The flat was being renovated when I was there..
4)The cleaner is polishing all the floor with a new wax polish. The floor is being polished with..
5) Who fed the baby? Better: Who is feeding the baby? Who is the baby being fed by?
6) What do they serve the custard with? What is the custard served with?
7) Did Jennifer organise a concert for charity? Was a concert for charity organised by Jennifer?
8)Somebody is cutting the grass in the garden.
The grass in the garden is being cut
Yes, all are correct, and for #5 I'd use the "is feeding" sentence since it's in present tense like the passive version. The first sentence in #5 is in past tense.
Good job.