Lesson 9
The Passive with Modals
Modal verbs in English can be used in passive forms. As with other passive constructions, the emphasis changes to the object that receives the action.
Modals in passive forms don't change. The sentence starts with the subject + the modal verb + "be" + the past participle.
HOW TO FORM

SUBJECT | MODAL VERB | BE | PAST PARTICIPLE | BY
Trees | must | be | planted | by students
Trees | should | be | planted | by students.

More examples:
Lights should be turned off when they are not needed.
Less water must be used to protect the environment.
Public transport can be used instead of private cars.
More bike lanes should be built in big cities.
Plastic bags should not be used in supermarkets.
Should more trees be planted in cities?
Renewable energy must be used more in the future.
Trees must not be cut down anymore.
Can air pollution be reduced by cycling more?
The pollution problem might be solved with new technology.