In a classroom, there were three students: Fiona, Marcellus, and Zhu. The teacher placed a blue notebook on the desk at the front and told the class that it contained the answers to the next day's test. The teacher then left the room, instructing the students not to peek inside. Fiona, who was really curious, couldn't resist and took a quick look while Marcellus and Zhu were focused on their own work. After Fiona sat back down, Marcellus went to the front to sharpen his pencil, briefly glanced at the blue notebook, but did not touch it. Meanwhile, Zhu was absorbed in writing an essay and didn't notice the interactions involving the notebook at all. Later, the teacher returned and found the notebook slightly open. Faced with the possibility of accusing a student of cheating, whom should the teacher question first based on the available information and why?
The teacher should question Fiona first about the slightly open notebook. Since Fiona actually went ahead and looked inside the notebook while her classmates were distracted, she demonstrated direct interest in the contents, clearly ignoring the teacher's instructions. Marcellus, on the other hand, although he approached the desk, merely glanced at the notebook and did not touch it, displaying no signs of having tried to open it. Zhu was preoccupied with writing an essay and had no interaction with the notebook or awareness of Fiona's actions, making Zhu the least likely suspect. Given Fiona's action of looking inside the notebook when she thought no one was watching, it follows that she is the most plausible individual responsible for leaving it slightly open.