In exponential smoothening method, which one of the following is true?
(a) 0 $\leq$ a $\leq$ 1 and high value of a is used for stable demand
(b) 0 $\leq$ a $\leq$ 1 and high value of a is used for unstable demand
(c) a $\geq$ 1 and high value of a is used for stable demand
(d) a $\leq$ 0 and high value of a is used for unstable demand