Correct answer: 1
The condition |z - 1| = |z + 1| describes the perpendicular bisector of the segment connecting the points 1 and -1 on the complex plane, which is the vertical line x = 0. The condition |z - i| = |z + 1| describes the perpendicular bisector of the segment connecting -1 and i, which intersects the first line at a single point, resulting in exactly one complex number that satisfies all three conditions.