The correct answer is B. Lead times .
Demand uncertainty becomes more difficult to manage when lead times are long or variable. Reducing lead time improves responsiveness, reduces exposure to forecast error, and helps improve customer service.
Reducing safety stock may actually reduce customer service unless uncertainty has first been reduced.
Exact extract: "Control of independent demand items becomes harder if there is any marked change in either lead time or demand. If lead time increases or becomes more critical for distribution or if demand increases suddenly stock-outs may occur with serious consequences." The same material states that safety stock is used to protect customer service when uncertainty remains. Exact extract: "Safety stock strategy for finished goods depends on at least four major factors: * The customer service level offered. * The predictability of demand. * The cost of carrying additional stock. * The cost of failure to supply." Therefore, reducing lead times is the most effective way to manage demand uncertainty and improve customer service.

Independent demand for components and subassemblies is not tied to the demand of a higher-level item.
These typically come from repair, maintenance, and service activities, where components are needed on their own rather than as part of a finished product.
"Independent demand... includes service/replacement parts and maintenance repair operating supplies."
- CPIM MRP Module C1-5