What is compound `(B)` and how is it formed ?

Explanation

Proceed reverse from `(C) ` to (B):
Join `C-2` to `C-8` by double bond. `7C-` atom ring in obtained (Numbering not for naming but to understand the problem) (Numbering for naming the compound.) (1,2- Dimethyle cyclohept -1-ene)
`D.U.` in `(B)=((2xx9+2)-16)/(2)=2^(@)`
`1 D.U.=` one ring
1 D.U.=one`(C=C)` bond
Total `D.U.=2`
Proceed from `(A)` and `(B)`
(Numbering for understanding the problem)