$$\left( 1,1,1,1,1,1 \right)$$；$$\left( 3,1,1,1 \right)$$；$$\left( 1,3,1,1 \right)$$；$$\left( 1,1,3,1 \right)$$；$$\left( 1,1,1,3 \right)$$；$$\left( 3,3 \right)$$． 
There are $6$ stairs, and you can walk for one or three staris each time. There are~\uline{~~~~~~~~~~}~different ways to walk the $6$ stairs. 

(a) $$2$$ 
(b) $$3$$ 
(c) $$4$$ 
(d) $$5$$ 
(e) $$6$$ 