1) I gave my friend Alex a good book as a present.
My friend Alex was given a good book by me as a present.
2) They look after the garden very well.
The garden is looked after (by them) very well.
3) We should water the house plants regularly.
The house plants should be watered by us regularly.
4) My dad told me this story long ago.
The story was told to me by my dad long ago.
5) Nobody listened to the speaker.
The speaker was listened to by nobody.
6) They can make some money by babysitting.
Some money can be made by them by babysitting.
7) I will show the children the new film.
The children will be shown the new film.
8) I will leave your train ticket on the table.
Your train ticket will be left by me on the table.