The monthly indexes for the first 11 months are [list of indexes]. What is the index for the last month?
a) Calculate the average of the first 11 months and use it as the index for the last month.
b) Use the median of the first 11 months as the index for the last month.
c) Extrapolate the trend from the first 11 months to estimate the index for the last month.
d) Set the index for the last month as the highest index among the first 11 months.