The Best Way to Deal with Respondents Not Knowing the Answer

Multiple Choice

The best way to deal with respondents not knowing the answer to a question is

A) perform sufficient exploratory research and questionnaire pretesting to understand what the population members are likely to know-or not know.
B) provide a "Don't know" response option.
C) increase the sample size.
D) All of these are correct.
E) None of these are correct.