Exercise for passive voice: special structures 27. You have to finish this work today 28.They are having to dig a big hole 29.People say that he is a spy 30.People think that the rich are not always happy3 31.It's possible to purify this water 32.It*s impossible to replace him 33.It*s essential to send this letter by airmail 34.It*s nessesary to keep your feet warm 3.It*s unnessary to learn the poem by heart