Consider the following statements about Cartesian coordinates: Which of the following is correct?

1. The first element of $(x, y)$ is the abscissa
2. On the x-axis the ordinate is zero
3. $(x, y)$ and $(y, x)$ denote the same point when $x \neq y$

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