kovarex:
I discovered that one of whites answers was wrong, and this problem actually leads to 10 000 years ko (or one more approach ko), not a direct ko. I re-checked with the book official answer, which is also 10 000 years ko, so I updated the prbolem.

semelis:
The combination beginning with B2+D2 has a bad refutation for C2+A2 continuation at the end with A5 that should be C3, as C3 after A5 kills.

posetcay:
B2-B1-B3-C2-D1 becomes seki, but is accepted as a correct answer.