why d is wrong? chemistry

In aqueous media, the following equilibrium occurs:

[Al(H2O)6]3+ → [Al(H2O)5(OH)]2+ + H+
[Al(H2O)5(OH)]2+ → [Al(H2O)4(OH)2]+ + 2H+
[Al(H2O)4(OH)2]+→ [Al(H2O)3(OH)3] + 3H+

In highly acidic solutions, the equilibria shift to the far left while in basic solutions, the equilibrium position shift to the right.

This reaction also occurs in highly alkaline medium:
[Al(H2O)3(OH)3] + 3OH- → [Al(OH)6]- + 3 H2O

You see, the equilibrium position is always affected by the concentration of acid or base.

Al3+
http://en.wikipedia.org/wiki/Aluminium_hydroxide

Aluminium Hydroxide had low solubility in water,that mean Al3+ would interact with hydroxide ion and form Al(OH)3,
though that salt is quite special that it can react with excessive OH- ion further to form soluble complex ion