It is difficult for the researcher to generate the answers if the questionnaire have "not sure" and "not applicable". In my opinion, depending on what the topic that the researcher want to get from the survey. Moreover, some of surveys the respondents can not answer because of they don't have any ideas about the products or services. Besides, if the respondents has been selected "not sure" or "not applicable" so, the results can not measurable to conduct the research.