19. Let f ( x ) be a function defined by  
Let p( x ) = a₀ + a₁ x + a₂x²+ … + a_nxⁿ+ … be the Maclaurin series of f ( x ).
Which of the following items is the value of a₃ ?
(A) –1
(B) 0
(C)
(D)
(E)1

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