What is the key challenge associated with selecting the weights in a weighted moving average forecasting model?

a$)$ Collecting sufficient qualitative data to supplement the forecast.

b$)$ Deciding the appropriate weight to assign to each time period.

c$)$ Identifying which months should be included in the model.d$)$ Ensuring that the total weight does not exceed $100\%.$

e$)$ Determining the exact mathematical formula for calculation.

f$)$ Calculating the average demand for products with highly erratic sales.