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. Therefore, 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?

• ATelecommunications signals sent along electrical wires can travel much farther than signals transmitted through fiber-optic before needing to be regenerated.  
• BExpanding its production of regenerators will require Light-Line to spend proportionately more on labor and materials.  
• CThe 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.  
• DThere are technologies that enable telecommunications signals to be transmitted without either wire or fiber-optic cable.  
• ESeveral manufacturers are developing regenerator technologies that will allow signals to be transmitted many times farther than at present before requiring regeneration.