The word "dialectic" refers to a method of reasoning and argumentation in which two or more opposing viewpoints are compared and analyzed, so the word that is most nearly the same in meaning to "dialectic" is option B, "argumentative."

"Dialectic" is often used in philosophy to describe a method of argumentation that involves the exchange of opposing ideas and viewpoints. This can be done in order to arrive at a deeper understanding of a particular concept or issue. The word "argumentative" also refers to the use of arguments to persuade or convince others of a particular viewpoint, so it is the closest in meaning to "dialectic."

Option A, "instructive," means providing knowledge or information, which is not directly related to "dialectic." Option C, "constructive," means building up or improving something, which is also not directly related to "dialectic." Option D, "destructive," means causing damage or harm, which is the opposite of "dialectic."