Answer:
1) The technique of calling out to people as they pass by and many ignoring the calls introduces "A) nonresponse bias" because those who choose not to respond to the survey may have different health and fitness habits compared to those who agree to participate, potentially biasing the results.
2) The fact that the survey is being administered by a health and fitness instructor at a local gym would likely lead to "B) response bias" because respondents might feel inclined to provide answers that they think the instructor wants to hear or that align with the gym's image, potentially biasing the responses.
3) The statement "a) True" is correct. In this scenario, the sample consists of the 70 people who agreed to complete the survey. These 70 individuals make up the group from which data is collected and analyzed to draw conclusions about health and fitness habits.