Development of the pancreas in an embryo into a dual gland that has both exocrine and endocrine functions begins when

A) insulin is produced and bathes stem cells.
B) a transcription factor stimulates progenitor cells to give rise to exocrine or endocrine cells.
C) a globin gene duplicates and gives rise to alpha and beta globin genes.
D) progenitor cells become stem cells.
E) the primordial pancreas splits into two parts, one exocrine and one endocrine.