20) I think that this type of sampling is known as non-probability sampling. Non-probability sampling is generally based on human choice; no one is forced to reply or even act. It does not target a specific audience. This is a voluntary survey and is highly selective, which is a characteristic of non-probability sampling.
21) In order to determine whether a survey question has bias, ask the following questions.
The question does not, as far as I can tell, leads one to think a certain way; the question simply asks what you (or I) think about a certain situation. The question is not preventing me from explaining my opinion of the subject at hand. The question is not asking too much at once. The question is pretty clear, and the question allows me to answer in any fashion that I want. This makes me believe that this is an unbiased question.