Maria Has Been Asked to Be a Subject in a Study

Multiple Choice

Maria has been asked to be a subject in a study to determine if additional vitamin A will promote the growth of healthy, strong fingernails Since she wants the study to be as close to the "ideal" nutrition intervention study as possible, she will want to be sure that:

A) only the researcher knows which participants receive vitamin A.
B) all of the participants are between 18 and 25 years of age.
C) her chances of getting vitamin A are better than those of anyone else.
D) half of the participants get something that looks like additional vitamin A but isn't.