Which of the following is a common ethical guideline suggested by the american psychological association?
a. participants may not withdraw once they start.
b. participants must be allowed to make an informed decision.
c. participants must not be deprived of food.
d. participants cannot be subjected to shock of any kind.
e. participants cannot be deceived about aspects of the research.

b. Participants must be allowed to make an informed decision.

Explanation:

There´s an ethical obligation to ensure people are capable of making an informed decision when participating in any research.

Valid consent requires no coercion, giving participants all relevant information, and guaranteeing they are capable of using that information to make a decision. APA's Ethics Code orders that psychologists to inform participants about the purpose of the research, it´s foreseen span and the details of the process.

think its caste system

explanation:

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.