Is It Important to Follow Up on Those Persons in a Survey

Is it important to follow up on those persons in a survey who did not return questionnaires mailed to them?

A) No, because high precision is not needed in questionnaire surveys.
B) No, because such delayed returns would be of doubtful value.
C) Yes, because the sample that has already returned the questionnaire may be biased.
D) Yes, because descriptive statistics require a large sample.