1. Pandas should be saved from extinction.

2. All traffic laws must be obeyed.

3. This broken window ought to be repaired.

4. The hotel guests should have been supplied with clean towels

5. Tomatoes can be picked before they are completely ripe

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