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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.