Can you explain where this structure can be used? Some of samples for the structure I'm reffering to are as it follows:
- These are messages sent by telegraph
- Talk about something connected to our topic
- Bring me the phones made in China.
For instance, in this example: "messages sent by telegraph". The way I thought it must be written is like this: "messages that were sent by telegraph". The examples considered, I guess we can omit "that be". But to make sure I wanted to ask is the way I comprehend it is accurate and where and when it is used?