Awadh (Oudh) was considered the "nursery of the Bengal Army" primarily due to the significant recruitment of soldiers from this region during the time of the British East India Company. The Bengal Army, a part of the East India Company's military forces, recruited a substantial number of soldiers from various regions, and Awadh was known for producing a large number of skilled and disciplined soldiers.

The soldiers recruited from Awadh played a crucial role in the Bengal Army, and their martial traditions and expertise were highly valued. The military prowess of the soldiers from Awadh contributed to the effectiveness and reputation of the Bengal Army during various military campaigns and conflicts in the Indian subcontinent.

So, the correct option is [2].