Which is the best explanation for why approximately 3,000,000, american women joined the workforce in 1918? a) they joined the workforce because of the effects of the great depression. b) they joined the workforce to offset the labor shortage caused by america's involvement in world war i. c) they joined the workforce because the 19th amendment made it illegal for employers to discriminate against females. d) they joined the workforce because the immigration act of 1917 caused a labor shortage in northern industrial cities.