When we are not sure that the obtained result of an experimental study is really attributable to our manipulation of the independent variable, we are questioning the __________ of the study

Mikael is a toddler who can stand on one leg, run with stiff legs, and kick a ball. Mikael is at least ____

a. 6 months old b. 12 months old c. 18 months old d. 24 months old

Jim came home from the office trembling, experiencing shortness of breath, irritable, unable to concentrate, and worrying about whether his business would still be open next week, despite the fact that his business was evidencing its highest profit ever. Jim's condition would most likely be diagnosed as

a. major depression. b. a phobic disorder. c. generalized anxiety disorder. d. a minor psychotic break.