Milton is retiring on his 65th birthday. He is eligible for Medicare and already receives Social Security benefits. How does he enroll in Original Medicare?

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.