Final answer:
Option A) Machine setup has the weakest linkage between activity and cost driver.
Step-by-step explanation:
The activity with the weakest linkage between activity and cost driver is option A) Machine setup, where the cost driver is the number of setups. The reason for this is that the cost of machine setup is not directly proportional to the number of setups. For example, if there are two setups, the cost may be the same as having just one setup, making the linkage weak.