He told us he _____ a concert _____ .

A．had attended ... three days before

B．attended ... three days ago

C．would attend ... since three days

D．was attending ... for three days

按照玻尔原子理论，氢原子中的电子离原子核越远，氢原子的能量________(选填“越大”或“越小”)。已知氢原子的基态能量为E₁(E₁<0)，电子质量为m，基态氢原子中的电子吸收一频率为ν的光子被电离后，电子速度大小为_____           ___(普朗克常量为h)。