How Did Bayliss and Starling Demonstrate That the Small Intestine

How did Bayliss and Starling demonstrate that the small intestine secretes chemical signals that stimulate the pancreas to respond to acid?

A) They injected acid into a dog's small intestine after dissecting away all the nerves.
B) They exposed a dog's small intestine to a cell extract made from a second dog's small intestine that had been exposed to acid.
C) They cut out a piece of the small intestine and exposed it to acid.
D) They injected pancreatic secretions from a dog previously exposed to acid into the small intestine of a second dog.
E) They injected acid into the pancreas after removing all of its innervation.