You have a monthly time series of toy sales, with an upward trend and obvious spikes in the last two months of each year. Which of the following will likely provide good forecasts?

a. The moving averages method, provided that the span is at least 12.

b. Regression with time itself and dummy variables for 11 of the 12 months.

c. Holt's exponential smoothing method, provided that optimal smoothing constants are used.

d. None of these choices are likely to provide accurate forecasts.