现代投资组合理论的基础是（）
参考答案：证券投资组合理论
—When Tom got to the examination room, he realized he ______ his pen at home.
－Oh, he is too careless.
A．had left
B．had forgotten
C．was leaving
D．leaves
A．U=vBl，流过固定电阻R的感应电流由b到d
B．U=vBl，流过固定电阻R的感应电流由d到b
C．U=vBl，流过固定电阻R的感应电流由b到d
D．U=vBl，流过固定电阻R的感应电流由d到b
vBl
vBl