P is the gall bladder which secretes only bile.
Q is the stomach. In the stomach, proteins are broken down. So proteases must be secreted. Also, hydrochloric acid is also secreted. This means that it has a high hydrogen ion (H⁺) concentration.
R is the pancreas which secretes all of the three enzymes: protease, lipase and amylase. Also, the pancreas secretes insulin to control blood glucose concentrations.
So A is the answer.