Final answer:
The popularity of trial-and-error over Linear Programming for Aggregate planning is not due to trial-and-error being quicker to solve or easier to model, but it is more flexible.
Step-by-step explanation:
The correct answer is c. Both a and b. Trial-and-error is not the preferred method for aggregate planning because it is quicker to solve or easier to model, but because it is more flexible compared to Linear Programming. Trial-and-error allows planners to quickly adjust their decisions based on feedback and make changes as necessary, unlike Linear Programming which requires precise mathematical calculations.