Let Q and R be expressed by ab*a and (ba)* respectively i.e Q={aa ,aba ,abba ……-and R=,Λ,ba baba,bababa…….-..aba is the only word in Q which can make a word in R, because the words in R don,t contain the?

(A) Single letter
(B) Double letter
(C) String
(D) Null string

Let Q and R be expressed by aba and (ba) respectively i.e Q={aa ,aba ,abba ……-and R=,Λ,ba baba,bababa…….-..aba is the only word in Q which can make a word in R, because the words in R don,t contain the?