Self-referential aptitude test

The self-referential aptitude test (SRAT) is a list of 20 multiple-choice questions, many of which are referring to each other. It was designed by James Propp, a professor of mathematics at the University of Massachusetts Lowellt.

Among them is this question, for example:

19. The answer to this question is:
   (A) A
   (B) B
   (C) C
   (D) D
   (E) E

Even though, the test has a unique solution (and in fact, this knowledge is really helpful for finding the answer to some questions).