In the Context of Public Opinion Polls,what Is Self-Selection

In the context of public opinion polls,what is self-selection?

A) a reference to the timing of public opinion polls that may skew survey results
B) a reference to the ability of respondents to decide whether to participate in surveys
C) a reference to long-term studies of the electorate invalidated by short-term biases
D) a reference to short-term studies of the electorate invalidated by long-term biases