Concept:To find out students’ preferences or opinions, the most suitable tool is a survey-based method.Explanation:Madam Nancy needs to know which teacher is liked best by most students.This information is a personal opinion.A questionnaire allows her to ask many students the same written questions.The students can choose their favourite teacher from the given options.An experiment, database, or observation would not directly gather students’ likes and opinions.Answer:C. Questionnaire