<s>[INST] context: Observational studies a. Descriptive studies b. Analytical studies Ecological or Cor relational, with populations as unit of study Cross- sectional or Prevalence, with individuals as unit of study Case- control or Case-reference with individuals as unit of study Coho or Follow- up with individuals as unit of study Experimental studies intervention studies Randomized controlled trials or clinical trials with patients as unit of study Field trials With healthy people as unit of study Community trials or community intervention studies with communities as unit of study Type of study Alternative name Unit of study Observational studies Descriptive studies Analytical studies Ecological Correlational Populations Cross- sectional Prevalence Individuals Case- control Case- refrence Individuals Coho Follow-up Individuals Experimental studies Intervention studies Randomized controlled trials Clinical trials Individuals Cluster randomized controlled trials Groups Field trials Community trials Community intervention studies Healthy people Communities [/INST] question: 'Groups' is the unit of study for? | options: A: Ecological study B: Cross sectional study C: Randomized controlled trails D: Cluster randomized controlled trails | answer: D </s>