Sadaharu: After B2D1C2, C1 or cut at B6 then C1 should work too and it's better than the correct answer's variation of seki because White's dead. Please refer to SGF.
yaya: Hi I.Z. as in a lot of other problems you posted, the correct solution is ruled out see .sgf. It's annoying, that you don't correct it, even, when you got a hint.
yaya: See .sgf, the line to W9 is ruled out, but Black is definetily dead after that, he has one liberty less. The best he can do instead is to make an eye with B8 to get a seki.
SGF