Selection bias occurs when the population has been divided into strata portions of the population are excluded from the consideration for the sample cluster sampling is used instead of stratified random sampling those responding to a survey or poll differ systematically from the nonrespondents

The correct option is B. portions of the population are excluded from the consideration for the sample.

Explanation:

Bias occurs when the data from an experiment is not correctly collected. While taking a sample, if we consider to take our data from only one part of a population and not from the rest then it will be considered as biased. For example, a researcher takes blood samples from just people who are his/her neighbours and make conclusions about the blood types of the people of the whole city.

answerclassical conditioning;

answer///unconditioned stimulus;