Blood is buffered within a narrow range around a pH of 7.4. This means that the pH of blood will remain close to 7.4 when _____.
moderate amounts of acid or base are added
moderate amounts of base, but not acid, are added
moderate amounts of acid, but not base, are added
moderate amounts of acid or base are added
moderate amounts of base, but not acid, are added
moderate amounts of acid, but not base, are added