Which describes a mixed economy? A) It is centrally planned. B) It is based on patterns from the past. C) It has elements of several economic systems. D) It is the free exchange between buyers and sellers.

What is the difference between an observational study and an​ experiment? choose the correct answer below. a. in an​ experiment, a treatment is applied to part of a population and responses are observed. in an observational​ study, a researcher measures characteristics of interest of a part of a population but does not change existing conditions. b. in an​ experiment, a treatment is applied to an entire population and responses are observed. in an observational​ study, a researcher measures characteristics of interest of an entire population but does not change existing conditions. c. in an​ experiment, a researcher measures characteristics of interest of a part of a population but does not change existing conditions. in an observational​ study, a treatment is applied to part of a population and responses are observed. d. in an​ experiment, a researcher measures characteristics of interest of an entire population but does not change existing conditions. in an observational​ study, a treatment is applied to an entire population and responses are observed.