If $P(x, y, z) = x^3 + y^3 + z^3 - 3xyz$, then consider: Which of the following is correct?

1. $P(x, y, z)$ is cyclic
2. $P(x, y, z)$ is symmetric
3. $P(1, -2, 1) = 0$

• ai, ii
• bi, iii
• cii, iii
• di, ii, iii