Answer:
A. the 10thhour of study will likely be less productive than the 3rd.
Explanation:
The law of diminishing returns is a point at which the level of benefits or apprehensions gained is less than the amount of energy or time that is invested.
So at the tenth hour, this law would be setting in, and the effectiveness of each additional unit of time decreases. So this hour will be less productive than the third hour.