subject + to be + past participle + rest of sentence + by agent

Marie baked a cake → A cake was baked by Marie

Drop the agent if it is:

• unknown
• obvious (vague)
• not important
• or you don't want to name it

Tenses

Verbs with two objects (ditransitive)

Some verbs that have two objects can make two different active sentences, and so two different passive sentences too:

• She gave a present to him

  → A present was given to him by her

• She gave him a present

  → He was given a present by her

Ask, offer, teach, tell, lend, promise, sell, throw

Summary

Use the passive when:

• you don't know the "doer" of the action, or the doer is obvious or unimportant
• you want to focus more on the action than the doer