TOEFL Listening: TPO-TOEFL听力TPO - 9QXU75L7L7GC82Q0R$

What is the main purpose of the lecture? A. To provide an example of a practical use of nanotechnology. B. To show the origins of the field of nanotechnology. C. To give a brief outline of the main concepts of nanotechnology. D. To explain the growing interest in nanotechnology research.