4. Chinese health officials investigated an outbreak of COVID-19 among a group of 300 individuals who attended a 150-minute worship event (Shen et al., 2020). Two groups of attendees traveled to the event by bus, the second of which carried an individual who had a SARS-CoV-2 infection (Bus 1, n = 60; Bus 2, n = 68). The at-risk individuals who rode Bus 2 were more likely to later be diagnosed with COVID-19 than those who rode Bus 1. COVID-19 diagnoses were also more common among those who rode Bus 2 than among all of those who attended the worship event but did not arrive by bus. What is the study design; A) Cohort, B) Case-control, C) Randomised control trial, or D) Cross-sectional