The Use of Coercion to Secure Participants for a Research

The use of coercion to secure participants for a research project can be a tricky issue.In which of the following scenarios is the coercion used to secure research participants considered ethical?

A) Megan, a Canadian undergraduate student, volunteered for a study in which she was asked to look at disturbing pictures and report her emotional responses because her professor made research participation a requirement of the course she was completing.
B) Chris, a prisoner at Warkworth Institution, complied with a request to be interviewed about his experience of prison violence because he was worried he would receive worse treatment from the guards if he refused to comply.
C) Brandon, a 14-year-old high school student, agreed to complete a survey on his beliefs and behaviour pertaining to drug use because the researcher was his English teacher's wife and he worried refusing to participate would upset his teacher.
D) Brent, a graduate student at a competitive university, witnessed a group of children shoplifting at the mall. Brent told the children he would turn them in and inform their parents of the shoplifting unless thy agreed to participate in his study on peer pressure.
E) Dr. Benton, an esteemed criminologist, responds to distress calls with police officers to interview persons who have been victimized. Knowing female victims of spousal abuse might be reticent to talk to her out of loyalty to their partners, Dr. Benton secretly tells the victims their husbands will not be charged if they cooperate with her.