2kW•h的电能可供一盏标有“220V 40W”的白炽灯正常工作______h.
:白炽灯正常工作时间:t=WP=2kW•h0.04kW=50h.
故答案为:50.
衡量城市化水平的重要标志是___________,它体现了发展水平_____________。
— She looks very happy. She have passed the exam.
— I guess so. It's not difficult after all. [ ]
A. should
B. could
C. must
D. might