A Team of Researchers Is Studying the Possible Effect of Parents

A team of researchers is studying the possible effect of parents taking child-rearing classes on children's behavioral well-being.When they test the relevant null hypothesis,they are assessing whether

A) sample data show that child behavior differed by whether parents took the classes.
B) parenting classes are actually the independent variable rather than the dependent variable.
C) the observed association between parenting classes and child behavior is the result of chance.
D) the observed association is actually explained by a confounding variable.