Which of the Following Instances of the Post Correspondence Problem

Multiple Choice

Which of the following instances of the post correspondence problem has a viable sequence (a solution) ?

A) {(b, bb) , (bb, bab) , (bab, abb) , (abb, babb) }
B) {(ab, aba) , (baa, aa) , (aba, baa) }
C) {(ab, abb) , (ba, aaa) , (aa, a) }
D) none of the above