The correct answer is option 2: Resumption of rent-free lands. This measure was associated with William Bentinck, who served as the Governor General of India.

Option 1, Introduction of postal system, is not directly associated with William Bentinck. The introduction of the postal system in India was actually started by Lord Dalhousie in the year 1854.

Option 3, Preservation of ancient monuments, is also not directly associated with William Bentinck. The preservation of ancient monuments gained significant attention during the British Raj, but it was not a specific measure introduced by Bentinck.

Option 4, Partition of Bengal, is also not associated with William Bentinck. The Partition of Bengal was carried out by Lord Curzon in 1905, long after Bentinck`s tenure.

Therefore, option 2 is the correct answer as it accurately reflects one of the measures associated with William Bentinck, which was the resumption of rent-free lands.