The answers for the blanks in the sentence description are double; single.
Explanation: Double blind procedures are used in research situations where there is concern that knowledge of the hypothesis or treatment conditions might skew the results in some way. Therefore it is best that the person receiving the treatment being studied or answering the questions on a survey for example does not know the aims of the study per se, and in the double blind situation the person directly responsible for administering the questions or gathering data is also not aware so they cannot introduce any bias. In a single blind situation the aims of the study in terms of hypothesis for example are not know to the participant themselves, but the researcher directly gathering the data and interacting with the research subjects will know the hypothesis or reasons for treatment in the study.
A Fertile Crescent, which is a crescent-shaped region that contains very
fertile land around the Tigris and Euphrates Rivers, parts of Asia
Minor, and the Nile River regions.
