1. This is not a well-written sentence. Participants are people; subjects are things. Probably the intent is to indicate that a smaller group of people are selected for some purpose, i.e. a study or an advanced class, from a larger group of people who are studying more basic subjects. For someone intending to study medicine, for example, foundational subjects might be chemistry or biology. But the exact meaning of "foundation" in that sentence is hard to decipher. 2. "Argument" in this context does not mean disagreement but rather a series of statements intended to persuade another of a particular point of view. 3. This sentence makes no sense at all. "React" is a verb and is misused. Perhaps the author of this sentence meant "reaction," but the sentence still would not make sense. A common usage of "characters" is people who play a role in a play, movie, or show.