No.722(Answers)

Black 1 is crucial.
If White 2, Black wins the capturing race with 3 and 5.
If White 2 at 5, Black wins with 3.

Black 1 allows White the vital point 2 and loses the race.

Black 1 and 3 are crucial, and can capture the three White stones.

If White 2, Black captures the four White stones with 3 and 5.

Black 1 is wrong.
With White 2, Black dies.