Insert prepositions. Keys: from, across, in, of, to, through, by.

1. Twisted pair cables were first used in telephone systems Alexander Graham Bell.

2. Electronic mail is a way sending messages and letters directly your computer to another computer.

3. You can send a letter your hundreds of friends all around the world a few seconds.

4. Subnetworks are arranged in three stages so that each call passes three subnetworks.

5. The cellular service lowers the cost of calls borders in the region.