When do we use the passive? We use the passive in the following cases:
Case 1: The thing done is more important than the doer.
e.g. A new supermarket was opened in our district last week.
Case 2: Both the thing done and the doer are important.
e.g. Algeria was colonized by the French.
Case 3: The doer is unknown.
e.g. A lot of articles are stolen in the supermarket every day.
Case 4: We don't want to mention the doer.
e.g. I was told that you had broken my glasses.
Here you've got some exercises: