50 to 200 copies. When conducting a questionnaire survey in graduate thesis, the appropriate number of questionnaires depends on many factors, including the purpose of the study, the representativeness of the sample, the complexity of the research questions, the requirements of data analysis and so on. For example, if the purpose of the research is exploratory, it needs a small number of questionnaires, such as 50 to 100, and in order to test the hypothesis or make further analysis, it needs 200 questionnaires.