B. When we use an active verb, we say what the subject does.
B1. When we use a passive verb, we say what happens to the subject.
B2. When we use the passive, who or what causes the action is often unknown or unimportant.
B3. If we want to say who does or what causes the action, we use by
B4. The passive is be (is/ was etc.) + past participle (done/ cleaned/ seen etc.): (be) done, (be) cleaned, (be) damaged, (be) built, (be) seen etc.
B5. Present Simple: Somebody cleans this room every day. vs. This room is cleaned every day.
B6. Past simple: Somebody cleaned this room yesterday. vs. This room was cleaned yesterday.
B7. Present Perfect: Active: Have/ has + done etc., Passive: Have/ has been + done etc.
B8. Past Perfect: Active: Had + done etc., Passive: had been + done etc.
B9. Present continuous: Active: am/ is/ are + (do)ing, Passive: am/ is/ are + being (done)
B10. Past continuous: Active: was/ were + (do)ing, Passive: was/ were + being (done)
C. Infinitive: Active: (to) do/ clean/ see etc., Passive: (to) be + done/ cleaned/ seen etc.
C1. Perfect infinitive: Active: (to) have + done etc., Passive: (to) have been + done etc.