Why were nomadic native american tribes in california unable to develop advanced inventions at the same time as mesopotamia?

Dr. redbull conducts a study to determine whether her new energy drink children perform better on spelling tests. she randomly assigns children to one of two groups: group 1 receives her energy drink and group 2 receives water. she then gives both groups a spelling test and compares the results. which of the following is true about this study? a. group 1 is the dependent variable and group 2 is the independent variable. b. this is a correlational study. c. group 2 is the experimental group. d. the independent variable is the type of drink the children receive.