Raul has no motivation to read the chapters from his biology textbook that were assigned for homework. According to the Premack principle, Raul could reinforce his textbook reading by doing ___

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 .

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

the factors that the economies of the muslim empires prosper were:

1- land trade routes-located between three continents  

2- sea trade routes

trade contributed to the spread of muslim empires, and with that islamic culture led to a growing feeling of internationalism resulted in the transfer of technology, science, and other cultural forms.