<prompt> The study of first choice for the assessment of an unknown or new disease when there is no etiological hypothesis is ___:Cohort study.Randomized clinical trials.Ecological studies.Descriptive studies.  <response>: Descriptive studies: Descriptive studies are used to describe a disease of unknown etiology.Steps of descriptive studies :Defining the population to be studied.Defining the disease under study.Describing the disease bya. Timeb. Placec. PersonMeasurement of disease.Comparing with known indices.Formulation of an aetiological hypothesis 