Reproductive health researchers conducted a study to test the causal hypothesis that history of smoking is a cause of infertility among women. They recruited 250 women aged 30-49 living in New York City recently diagnosed with infertility at the Columbia University Fertility Center. They additionally recruited 300 women aged 30-49 living in New York City who were not infertile. All 550 women were asked about past history of smoking. Those who reported never smoking were categorized as “No History of Smoking,” while all others were categorized as “History of Smoking.” Use the table below to answer the following questions. Infertile Fertile Total History of Smoking 77 52 129 No History of Smoking 173 248 421 Total 250 300 550 a) What type of study design (RCT, observational cohort, case-control, cross-sectional, etc..) is this? How do you know?