|Question 16Math

Question

Prompt
To investigate the effect of magnesium supplementation on the sleep quality of adults, a researcher selected adults at random from a community center to participate in a study. The researcher first measured the sleep efficiency of each participant. Each participant was then randomly assigned to take a magnesium supplement or a placebo each day for weeks. At the end of the weeks, the researcher measured the sleep efficiency of all participants again and found that the magnesium supplement caused statistically significant improved sleep quality for the adults at the community center. What feature of this study allowed the researcher to conclude that the magnesium supplement caused the improved sleep quality?
There were more than participants in the study.
A
The participants were selected at random from the community center.
B
The sleep efficiency of each participant was measured again at the end of weeks.
C
Each participant was randomly assigned to take a magnesium supplement or a placebo.
D