Church's thesis equates the concept of computable function" with those functions computable by, for example, Turing machines. Which of the following is true of Church's thesis?
A. It was first proven by Allan Turing.
B. It has not yet been proven, but finding a proof is a subject of active research.
C. It can never be proven.
D. It is now in doubt because of the advent of parallel computers.
E. It was never believed, but was assumed in order to simplify certain undecidability results.