The argument: Therefore, by replacing the old equipment with this new equipment, factories will quickly realize cost savings.

To undermine this, we need to show that there won't be cost-saving as mentioned.

A. Workers who use both the old and new equipment report greater difficulty switching to the old equipment from the new equipment than switching to the new equipment from the old equipment. - Switching pattern is not relevant to the argument

B. Manufacturing costs for the new equipment are similar to those for the old equipment. - Manufacturing cost - out of scope.

C. The number of factories that use the new equipment has increased every year for the past 5 years. - No of factories is not relevant to the argument.

D. The more time an employee has spent using the old equipment, the more expensive it is to teach that employee to use the new equipment. - Yes. so if new equipments are installed then the expense to teach the employees will be high.

E. New workers can learn to use the new equipment in the same amount of time that it takes them to learn to use the old equipment. - Time is not relevant to the argument.

Answer D