A nutrition scientist designs a study in which he assigns 100 people to the treatment group and 100 people to the control group. Although the scientist knows each person's group assignment, the subjects are not aware of their group placement. This is an example of .a. double-blind study
b. uncontrolled study
c. single-blind study
d. biased study

Option C, single-blind study

Explanation:

In a single blind study, the researcher is aware of the experimental group in which the subject is placed. However, the subject is unaware of its placement. Such kinds of experiments are conducted to reduce the risk of errors or variation in participant’s response, if they come to know the group type in which they are placed.  

In a double blind study both the researcher and the subject of the experiment are unaware of the groups in which the subject is placed while conducting the experiment

Hence, option C is correct

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.

the framers of the constitution insisted that federal judges be nominated instead of elected due to their desire to have judges above the shifting whims of the masses.

the hope, whether achieved or not, was that federal judges would only be beholden to the law and that by not having judges be elected, they would be protected if that law dictated an outcome that ran counter to popular opinion.