This question is asking what hormone causes contraction of the bladder & where is it produced. CCK is the hormone and it's produced by the I cells in the duodenum and jejunum in response to fatty acids and amino acids. The only answer choice that made sense was the one that included small intestine.

VIP (the only other answer that had any part of the small intestine in it) would cause watery secretions, not gallbladder contraction.