What are the roles played by active population in the development of the country??​

1u.s. history question! question: how did world war ii change the united states' position in world affairs? i need good explanation to support the answer otherwise i get docked points. real answers only ! you! : )

Pj conducts an experimental study on the effects of soft music during high stakes science testing. he randomly assigns students at the school. in one condition he does not provide music for testing while in the other group he does provide the music. he administers a pretest at the beginning of the year and a posttest at the end of the year. pj’s design is best described as a: a.static group comparisonb. pretest-posttest control group designc.control-group-time-series designd. nonrandomized control-group pretest-posttest design

At what age must a person begin receiving their roth 401(k) payments?