Final answer:
The statement is true as variability in setup times, processing times, interruptions, and job changes are major reasons for scheduling difficulties in operations management.
Step-by-step explanation:
A major reason for scheduling difficulty indeed is the variability in setup times, processing times, interruptions, and changes in the set of jobs. So, the answer to the question is A) True. In operations and production management, the variability of such factors greatly complicates the task of creating an efficient and effective production schedule. For instance, if setup times vary significantly among different jobs or machines, it may be difficult to predict how long it will take to switch from producing one product to another. Similarly, variable processing times can lead to delays if a job takes longer than expected. In addition, unforeseen interruptions like equipment malfunctions can throw off a schedule, and changes in job priorities or due dates can force a reorganization of the production schedule. These challenges are central to the field of operations management, where various strategies and tools are employed to create flexible and resilient scheduling systems.