Final answer:
Gleaning refers to the act of gathering leftover grain from the fields after the harvest, a task historically performed by the poor as depicted in Millet's 'The Gleaners'. It is distinct from other agricultural labor such as cotton picking. (option b is the correct answer).
Step-by-step explanation:
Gleaning is b. gathering leftover grain after the harvest. This practice has a long history and is often associated with agriculture and the care of land and crops. It is a process where after the main harvest, individuals, usually the poor, would go through the fields to collect any bits of grain left behind to use for their sustenance.
This concept was immortalized in the painting 'The Gleaners' by Jean-Francois Millet in 1857, which highlighted the plight of the rural poor. In contrast, cotton picking, as exemplified by the practices during the era of slavery, was a systematic and labor-intensive process that involved harvesting the cotton bolls from the plant and was a completely different agricultural activity from gleaning.