Which of the following is wrong about the gastrointestinal hormones?
A.
由散在于黏膜层的内分泌细胞分泌 they are secreted by the endocrine cells in the mucosa layer of GI tract
B.
All the gastrointestinal hormones are peptides.
C.
exist only in the GI tract
D.
regulate both the motility and serection of the GI tract