Computer manufacturers and retailers tell us that the complexity involved in connecting the various components of personal computers is not a widespread obstacle to their use, but this is wrong. Customers who install accessories to their personal computers have to take full responsibility for the setting of jumpers and switches to satisfy mysterious specifications. Many accessories require extra software that can cause other accessories to stop working; adding a modem, for instance, may disable a printer. Which one of the following, if true, most seriously weakens the argument? ['Computer manufacturers rarely take into account ease of installation when they are designing programs or accessories.', 'A personal computer is usually sold as part of a package that includes accessories and free installation.', 'Software for accessories can often be obtained for free.', 'Personal computer instruction manuals usually explain the purposes of the jumpers and switches.']