A track coach asks half of the athletes, chosen randomly, to try wearing a new type of shoe. Later the coach compares results for those wearing the new and old shoe types. What is the independent variable in this experiment?

Fluid intelligence consists of ________

a. the kind of intelligence that gives one the ability to do arithmetic and define words. b. intellectual abilities that develop from one's environment. c. specific knowledge learned through education and life experiences. d. the ability to use new information to solve problems.

Roughly half of a newborn's sleep time is spent in the ____ stage

a. rapid eye movement (REM) b. nonREM-1 c. nonREM-2 d. nonREM-3