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
Ngữ Pháp:
+) Have to do st -> St have to be done: phải làm gì
+) 
=> bị động: S + can't + be + P2
+) It's necessary to + Vinf
--> bị động: S + should/ must + be +P2
27. You have to finish this work today
=> This work have to be finished today.
28.They are having to dig a big hole
=> A big hole is having to be digged.
29.People say that he is a spy
=> He is said to be a spy.
30.People think that the rich are not always happy
=> It is thought that the rich are not always happy.
31.It's possible to purify this water
=> This water can be purified.
32.It*s impossible to replace him
=> He can't be replaced.
33.It*s essential to send this letter by airmail
=> This letter must be sent by airmail.
34.It*s nessesary to keep your feet warm
=> Your feet should be kept warm.
3.It*s unnessary to learn the poem by heart
=> The poen shouldn't be learnt by heart.
