[求助]JJ mice climbing

hujin2001

count the number of ways for a mice climbing from level 1 to level 5..Pict belowed
A, 16( maybe)
B. 25(maybe)
C 50
D 3^5
E 4^6
摎埬:16          

 o        level 1
                 /\        level 2
                /\/\       level 3
               /\/\/\      level 4
              /\/\/\/\     level5
the jj author's answer is 4^2=16. why it's 4^2?  please advise.  Thanks.

yuching730

WUPA第八篇有解………