Answer:
Option (a) is correct.
Explanation:
According to the law of diminishing marginal productivity, if there is an increase in the input in the production of a certain commodity then as a result there is an increase in the output of that commodity, initially but further increase in the input will have no impact on the output of the commodity or will have a negative impact.
In our case, when farmer hires 3rd worker, the output increases by 1,400(4,400-3,000) bushels. According to the law of diminishing marginal productivity, if he hires 4 workers then there is an increase in the output but less than the 1,400 bushels.
This condition will be satisfied in the option (a), where output increases by 1,200 bushels.