Which of the Following Is True About Response Formats for Survey

Which of the following is true about response formats for survey questions?

A) It is always better to include an explicit "don't know" option for opinion questions.
B) For measuring attitudes, the optimum number of categories is four.
C) Because of their explicit meaning, the numerical values of rating-scale endpoints (e.g., 0 to 6 or -3 to +3) are arbitrary.
D) Adjectival labeling of each response category can clarify the meaning of rating scales.