Active/passive voice

We use a passive verb to say what happened to the subject:
- This house is quite old. It was built in 1930.
- Two hundred people are employed by the company.

When we use the passive, who or what causes the action is often unknown or unimportant.
- A lot of money was stolen by robbery.(somebody stole it but we don't know who)
- Is this room cleaned every day. (does somebody clean it? - it's not important who)
 

The passive is be(is/was/have been etc.) + the past participle (done/cleaned/seen etc.)

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