An explicit detail refers to something that was directly expressed in the text, while an implicit detail would be indirect, and implied. All of the other choices are inferences based on his body language and whatnot. While choice C has direct evidence, given that he is sitting in a "hard chair" and he describes the room as "a cold room in University Administration."
The reason why the boy's father doesn't tell the boy to leave is : C. The father is unconscious I think it's pretty much self-explanatory. No father will let danger come to his son if he can help it
