Explanation:

Alright, let’s break this down clearly:

- Option 1: 01 April 2005. This is not the date the Act came into effect—it’s when the bill was first introduced.

- Option 2: 11 March 2006. No major development for this law happened on this date, so this isn’t correct.

- Option 3: 21 May 2005. This marks the date when the bill received Presidential assent, but law didn’t come into force yet.

- Option 4: 26 October 2006. This is when The Protection of Women from Domestic Violence Act, 2005, actually came into effect and people could use its protections and mechanisms.