For predicting the straight-line trend in the sales of scooters (in thousands) on the basis of 6 consecutive years data, the company makes use of 4-year moving averages method. If the sales of scooters for respective years are a, b, c, d, e and f respectively, then which of the following average will not be computed?

a) \(\frac{a+b+c +d}4\)

b) \(\frac{b+c +d+e}4\)

c) \(\frac{a+c +d+e}4\)

d) \(\frac{c +d+e+f}4\)