The thesis statement will always be the heart of the essay, which is the main/critical point.
The correct answer is B, The thesis statement of an essay
In essays including literary essays, the thesis statement is the main point that is developed through arguments and evidence. Because of this, the thesis statement is always a critical position about a topic, material, issue, etc. In the case of literary essays, the thesis statement refers to the critical point of the author about a literary work or a section of it and that reflects the interpretation of the author. Additionally, the thesis statement is considered as the most important element in essays because it is the focus and guideline for it. The previous ideas imply, in the case of "the critical point you want to make about a piece of literature" the concept described is the thesis statement.