Answer: b. Participants must be allowed to make an informed decision.
Step-by-step 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.