If addition of a substantial quantity of acid to a solution

If addition of a substantial quantity of acid to a solution resulted in only a moderate change in the pH of the solution, which of the following is likely true? a) The solution was pure water before the acid was added. b) The solution contained a buffer. c) The solution was strongly basic before the acid was added. d) The solution contained a moderate concentration of H+ before the acid was added. e) There is more than one correct answer choice.

Solution

after adding substantial quantity of acid to a solution the p?H channge is moderate then the effect should be by a buffer. so the answer is the solution contained a buffer