Recent research shows that sound change (pronunciation shift) in a language is not gradual. New sounds often emerge suddenly. This confounds the classical account of sound change, whose central tenet is gradualness. Since this classical account must be discarded, sound-change theory in general must also be. Which one of the following, if assumed, does most to justify the argument's conclusion?
A: The emergence of new sounds appears to be random.
B: All theories of sound change rely heavily on the classical theory.
C: For most languages, historical records of their earlier stages are scarce or nonexistent.
D: The data on which the classical account of sound-change theory was based are now known to be inaccurate.
Choose A, B, C or D as your solution.
B