State the type of voice in the sentences. (Оп редели тип залога в следующих предложениях.)

1. This chair has been made by students.

• Active voice
• Passive voice

2. The letters were sent to Moscow yesterday.

• Active voice
• Passive voice

3. The boxes have been brought by the postman.

• Active voice
• Passive voice

4. The song was written by a famous song-writer.

• Active voice
• Passive voice