Which of the Following Statements Is True

Which of the following statements is true?

A) Biologists have a good idea of the number of species on Earth.
B) One factor that limits our ability to predict the number of species that will go extinct in the next 50 years is our lack of knowledge about the geographic ranges of species.
C) If humans did not exist, no species would go extinct in the next 100 years.
D) The process of determining whether a species is extinct is not difficult.
E) None of the above