Hello!
Correct answer is A: generalization
An argument is a construction of reasoning and examples that support your main thesis and, as it is well- structured and developed, it is not a simple statement.
A conclusion is the union of all your arguments, in a general way, so as to support your standpoint; but it would not work with a simple statement and it has ideas in which that we can delve deeper.
A plot continues being a short story or the main facts that happen in something; it is also a complex structure.
Now, a generalization, like the conclusion of a syllogism, for example, would be a simple argument that englobes in a very general way another arguments that are difficult to understand. The generalization is contextualized and it's a very basic idea made for us to understand better some things.
Hope this helps