Among the options provided, the statement that represents a setback for mixed economies is:
Government oversight is expensive.
While mixed economies attempt to balance government intervention and free-market principles, the cost of regulation and oversight can be a significant setback, as it may lead to inefficiencies and increased public spending.
The other options suggest issues more aligned with other economic systems or do not reflect the typical challenges of mixed economies directly. For example, monopolies and limited consumer choices can happen in various economic contexts, but they may not be inherent drawbacks of mixed economies specifically.