Answer:
doing something enjoyable after reading
Explanation:
The Premack principle -
The principle was given in the year 1965 by David Premack .
According to Premack principle ,
The method to change the activities from time to time , makes the activity less boring and doable .
Hence , from the scenario of the question ,
Raul finds the biology book very boring and unexciting to study , but he does not have any option he need to study the book , so the best approach in order to make the subject interesting by switching things .
He can study for on hour and then go to play or do something interesting for 30 mints , the method will make him study the subject in a better manner .