What does the following recursive algorithm display?

writeBack$($in s:string$)$

$$ if $($s is empty$)$

$$ return

$$ else

$\{$

$$ write the first character of s

$$writeBack$($the string beginning at the second character of s$)$

$\}$

a$.$

nothing

b$.$

the string s backwards

c$.$

the string s

d$.$

the first character of s a number of times equal to the length of s