（单选题） Which of the following statements about secretion is true
选项：

A: The membrane of a secretory vesicle will fuse with（融合） the plasma membrane when it discharges its contents to the cell's exterior.
B: Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received by the cell.
C: The signal sequences of proteins destined for constitutive exocytosis ensure their packaging into the correct vesicles.
D: Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.