Which of the Following Research Projects Would Likely Be Called

Which of the following research projects would likely be called unethical?

A) Asking parents and teachers for permission to observe parent-teacher conferences in order to study parent-teacher interactions
B) Asking all parents in a school district to complete an anonymous survey about their satisfaction with the district's new online lunch payment system
C) Putting a suggestion box in the school cafeteria so that students can offer about meals
D) Using a hidden camera to record parent-teacher conferences without parent permission but with teacher permission, in order to study how teachers interact with parents and make recommendations for how they can improve their communication strategies