please help me i dont know how to answer this...

Answer:
A.
.1. B
.1. B2.A
.1. B2.A3.C
.1. B2.A3.C4.A
.1. B2.A3.C4.A5.B
.1. B2.A3.C4.A5.BB.
.1. B2.A3.C4.A5.BB.1. A
.1. B2.A3.C4.A5.BB.1. A2.C
.1. B2.A3.C4.A5.BB.1. A2.C3.B