No.692(Answers)

Black 1 is crucial.
If White 2, Black lives with 3.

Black 1 allows White to get a Ko with 2 to 6.

Black 1 first, and then Black 3 is crucial.
White can create a Ko with 4 to 8, but it is an unfavorable Ko for White.

Black 1 is wrong.
White survives with White 2.