A language with string manipulation facilities uses the following operations.
head(s)- returns thefirst character of the string s
tail(s) - returns all but the first character of the string s
concat(s1, s2) - concatenatesstring s1 with s2.
The outputof concat(head(s), head(tail(tail(s)))) , where s is acbc is

A

ab

B

ba

C

ac

D

aa