Computer manufacturers have sought to make computer chips ever smaller, since decreasing the size of a computer' s central processing unit (CPU) chip -- without making that CPU chip any less sophisticated -- will proportionally increase the speed of the CPU chip and the computer containing it. But since CPU chips cannot be made significantly smaller without decreasing their sophistication, computers cannot currently be made significantly faster. Which one of the following is an assumption on which the argument depends? ['If both the size and the sophistication of a CPU chip are decreased, the speed of that chip will decrease.', 'Even if CPU chips are made slightly less sophisticated, they cannot currently be made much smaller.', 'Computers cannot currently be made faster unless their CPU chips are made smaller.', 'Few, if any, computer manufacturers believe that computers can be made significantly faster.']