During ingestion of a meal, contraction of the gallbladder is thought to be regulated by

Fatty acids in the lumen of the duodenum, from the ingested food, stimulate endocrine cells to release the cholecystokinin (CCK). CCK stimulates contractions of the gallbladder. Also, acidic chyme (partly digested food) in the lumen of the duodenum stimulates other endocrine cells to release the secretin. Secretin stimulates duct cells in the liver to release bicarbonate into the bile.

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.