Which of the following citizens are required to sign up for selective services? A males 18-25
B. males and females 18-25
C males 25 and older
D males and females 25 and older

Using mr smith and his id, identify two potential internal validity threats that might affect the a—b design. tell me how that threat might impact conclusions in the a—b design. note #1: you cannot use maturation (since i already did that one for note #2: there are some mr smith id threats that won’t have much impact in a single case design.