Answer: Through the use of close-ended questions, for example a question with a YES/NO answer.
Explanation:
Close ended questions are questions in which a participant has already been provided with options to a question, and so the participants must choose from the options and cannot give an answer outside the options given.
Using this kind of question to modify the database schema would be helpful.
Therefore, in order to affirm that the volunteers are not allergic to dogs or cats, the close ended question "are you allergic to dogs or cats" can be used. The volunteers would be provided with a yes or no answer which they must choose from.
This would help in modifying the database schema while affirming whether the volunteers are allergic to dogs or cats.