No.700(Answers)

Black 1 and 3 are crucial.
If White 4 and 6, Black lives with 5 and 7.

Black 1 is crucial.
If White 2, Black 3 is brilliant.
If White 4, Black gets a Ko with 5 and 7.

If White 2, Black gets a Ko with 3 and 5.

Black 1 is wrong and lets White live with the moves to White 6.