There are some criteria which an ideal antacid should fulfill. Some of the criteria are given below: [P]: The antacid should be absorbable orally and should buffer in the pH range of 4'6. [Q]: The antacid should exert its effect rapidly and should not cause a large evolution of gas. [R]: The antacid should not be a laxative or should not cause constipation. [S]: The antacid should react with the gastric acid and should inhibit pepsin. Choose the correct combination of criteria for an ideal antacid.