GRE Reading Comprehension: Kaplan-GRE阅读Kaplan - HA1G21ICUN233UF2G$

According to the passage, all of the following statements are true EXCEPT: A. Medical nanotechnology is a field of nanotechnology that is entirely biological in practice. B. Nanotechnology has already led to medical practices that are currently in use. C. There are valid concerns regarding the use of nanotechnology. D. Some of what happens on the nanoscale is naturally occurring. E. Gene therapy is a result of medical nanotechnology.