1) Kate's plants look green and fresh (water) Kate has watered her plants.
2) Mum's bedroom window is opened. (open) Mum has opened her bedroom window.
3) Mary knows what the film is about. (watch) Mary has watched the film.
4) My friends know what the British Museum's like. (visit) My friends have visited the British Museum.
5) Emma's hair is clean and shiny. (wash) Emma has washed her hair.
6) The Smiths know where they'll spend their weekend. (decided ) The Smiths have decided where they'll spend their weekend.
7) Jake's supper is ready. (cook) Jake has cooked supper.
8) Mary's friends are in London. (arrive in) Mary's friends have arrived in London.
9) Peter is wearing different clothes now. (change) Peter has changed his clothes.
10) The sisters are enjoying a wonderful new book. (discover) The sisters have discovered a wonderful new book.