Which of the following statements about vocabulary building is correct? a. supporting sentences should "prop up" a topic sentence, while topic sentences should relate to the statement. b. the thesis statement belongs at the bottom of the pyramidal writing structure, while topic sentences belong at the top. c. topic sentence should state what you want to say about the overall topic. d. a topic sentence is typically placed at the end of the first paragraph.

I would say the correct answer is A. Supporting sentences should "prop up" a topic sentence, while topic sentences should relate to the statement.
B is incorrect because the opposite is true. C is incorrect because that is the job of a thesis statement - a topic sentence states what you want to say in a particular paragraph. D is incorrect because a topic sentence is usually placed in the beginning of a paragraph - this sentence refers to the thesis statement.