Based on the piece of Bach - Prelude in C (BWV 846).Why do those B- flats at the end not take us away from the Key of C major ( why arent they part of a modulation to F major)?

Question

(A) No perfect cadence in the key of F
(B) F major chord is comprimised of F,A and C and B flat isnt one of them
(C) Not enough F's
(D) The B naturals contradict the B flats
(E) Because of the C bass note running all the way through these last bars

Answer 1

Definitely B