Answer:c)Designing the survey so that subjects are not forced to answer one question before going to the next.
Explanation: when someone is voluntarily participating in a survey especially if it deals with sensitive information they shouldn't be forced to answer a question before they move to the next, but they should be given a freedom to choose to answer only those questions they feel comfortable to answer.
If that is not the case the survey will be forcing a person to disclose an information they don't want to disclose.