Final answer:
The description corresponds to an experiment because it involves the active manipulation of the independent variable, which is the injection of vitamins to assess their impact on a disease.
Step-by-step explanation:
The given description corresponds to an experiment rather than an observational study. In the mentioned study, 356 women with a particular disease were injected with vitamins to determine the effect on the disease. This intervention, where subjects receive a treatment and are monitored for outcomes, indicates an experiment where researchers manipulate the independent variable and observe the effects of this manipulation. This differs from an observational study where researchers would record naturally occurring phenomena without intervention. The key characteristic of an experiment is the deliberate and controlled application of a treatment, which is present in this scenario where vitamins are being injected to assess their impact.