In recent years, networks of fiber-optic cable have been replacing electrical wire for transmitting telecommunications signals. Signals running through fiber-optic cables deteriorate, and so the signals must be run through a piece of equipment called a regenerator before being transmitted farther. Light-Line is the leading manufacturer of signal regenerators. Ttherefore, Light-Line is one of the companies that will most benefit if new long-distance fiber-optic telecommunications networks are constructed. Which of the following, if true, casts the most doubt on the prediction about Light-Line's prospects? ['Several manufacturers are developing regenerator technologies that will allow signals to be transmitted many times farther than at present before requiring regeneration.', 'The volume of signals that a fiber-optic cable can carry is several thousand times greater than the volume that can be carried by an electrical wire of similar size.', 'Telecommunications signals sent along electrical wires can travel much farther than signals transmitted through fiber-optic before needing to be regenerated.', 'Expanding its production of regenerators will require Light-Line to spend proportionately more on labor and materials.']