Researchers conducting web-based research have trouble controlling who actually answers their on-line questionnaires, which places limits on their research due to the possibility of a. biased samples. b. the barnum effect. c. researcher bias. d. research participant bias.

Researchers conducting "'web-based research" have trouble controlling who actually answers their "on-line questionnaires", which places limits on their research due to the possibility of research participant bias.

Explanation:

Most web-based researches are subject to bias because the 'participant' in the research, i.e. the one who answers the questions is unknown to the researcher and may not be as serious with his answers. The credibility of such research is often questionable. The researcher may not always fetch answers from the expected age group, or may get answers from anyone who doesn't fit in the criteria specified by the researcher. This makes the answers biased towards the preferences of the person who isn't even eligible to participate in the research.

Joe ran 130 yards because 3 feet make 1 yard so using this ratio 390 feet make 130 yards.