黄磷应存放在水中，原因是（）。
参考答案：水可避免黄磷与氧接触，防止黄磷与氧结合发生自燃
The day _____ I stayed with a disabled boy is never to be forgotten. [ ]
A. which
B. that
C. when
D. in which
已知交流电电压U=380V，功率=1000W，则负载电阻R为（）Ω。
A.380
B.220
C.144.4
D.190
