In a large city school system with 20 elementary schools, the school board is considering the adoption of a new policy that would require elementary students to pass a test in order to be promoted to the next grade. the pta wants to find out whether parents agree with this plan. a) if they put a big ad in the newspaper asking people to log their opinions on the pta web site what kind of bias might they encounter. response bias due to desire to give acceptable answersnonresponse bias bias due to the use of a voluntary response samplebias due to a poor sampling frame resulting in undercoverageno biasb) if they randomly select one of the elementary schools and contact every parent by phone, what kind of bias is there? bias due to the use of a voluntary response sampleresponse bias due to desire to give acceptable answers undercoverage bias due to a poor sampling frameno biasnonresponse biasc) suppose they randomly select 20 parents from each elementary school. send them a survey, and follow up with a phone call if they do not return the survey within a week. what kind of sampling was done? stratified samplingconvenience sample simple random samplingvoluntary response sample