People should save pandas from extinction.
⇒ Pandas from extinction should be saved.
People must obey all traffic laws.
⇒ All traffic laws must be obeyed.
Someone ought to repair this broken window.
⇒ This broken window ought to be repaired.
Someone should have supplied the hotel guests with clean towels.
⇒ The hotel guests with clean towels should have been supplied.
People can pick tomatoes before they are completely ripe.
⇒ Tomatoes can be picked before they are completely ripe.
Công thức:
S + model verb + V + O
⇒ S + model verb + be + P2 + by + O
S + modal Verb + have +P2
⇒ S + modal Verb + have been +P2