You see a woman student standing in front of the student center, now and then stopping other students to ask them questions. She says that she is collecting student opinions for a class assignment. Explain why this sampling method is almost certainly biased. This is a convenience sample with a voluntary response bias. She is only getting opinions from students who are at the student center at a certain time of the day. This is an observational study. She is observing people's opinions rather than assigning them a stance on the issue. This is a voluntary response sample. She is only getting responses from people with strong opinions. This is a sample survey. She is only getting opinions from a few students when she should be asking everyone's opinion.