Step 1: Policy decision.
The Bihar government under CM Nitish Kumar decided in 2006 to enhance reservation for women in Panchayati Raj Institutions from the baseline one-third to 50%.
Step 2: Significance.
Bihar became one of the earliest states to provide half the seats to women across PRIs—Gram Panchayat, Panchayat Samiti, and Zila Parishad—strengthening grassroots representation.
Step 3: Distinguish later years.
2009/2011 saw subsequent elections and similar moves by other states, but Bihar’s policy shift dates to 2006.
Step 4: Conclude.
\[
\boxed{\text{2006 (Option B).}}
\]