Explanation:

The stomach releases gastrin in response to a falling pH in order to initiate acid (HCl) production in the stomach. On the other hand, CCK production from I cells in the small intestine and gallbladder are inhibited via negative feedback by luminal acid from the stomach. Low pH directly inhibits CCK release because a drop in luminal pH below 4 stimulates somatostatin release, which in turn blocks the release of CCK.