1. Investigators analyzed data from the U.S. CDC to identify factors associated with inadequate sleep (Liu et al., 2014). Participants were randomly selected to answer questions about their sleep habits and demographic characteristics. Overall, 65% of the study population reported meeting the recommended healthy sleep duration of at least 7 hours each night. Respondents who were aged 65 years or older were more likely to report sleeping at least 7 hours relative to younger respondents. What is the study design; A) Cohort, B) Case-control, C) Randomised control trial, or D) Cross-sectional