The text is for questions 24 - 28.

    A cell phone is a great gadget in this modern world. What is a cell phone? A cell phone is actually a radio in certain way. Like a radio, by a cell phone we can communicate to other people in real time. Million people use cell phone for their communication. Even nowadays, people use cell phones to communicate in voice, written and data. Alexander Graham Bell is the person who makes great change in the way people communicate to each other. He invented a telephone in 1876. While wireless radio was formally known in 18994 presented by Guglielmo Marconi. By these two technologies, then a cell phone was born. However, do you know how actually cell phones work?

    This short explanation on how a cell phone work is really wonderful. A cell phone or in long term 'cellular telephone' works by transmitting signals of radio to towers of cellular. The towers are networked to a central switching station. The connection usually uses wire, fiber optic-cables, or microwave.

    Then the central switching station which handles calls in certain given area is directed connected to the wire-based telephone system. Cellulars are pick up by the towers and relayed to another cellular telephone user or the user of wire-based telephone network the towers vary in the capacity and capability to receive signals. Some can receive the signal from short distance and the others can receive more distance. However, there are usually more than one tower in certain given area so that the system can handle the increasing telephone traffic.

24. What is the main idea of paragraph three?