b)the results of the survey cannot reliably be extended and generalized.
Step-by-step explanation:
Voluntary sampling is a type of convenience sample; it is convenient for the researcher to perform.
However, voluntary sampling can lead to bias; usually only people who feel strongly one way or the other about the survey will volunteer to be members of a sample.
Since there is a possibility of bias, the results of the survey cannot reliably be extended and generalized.
