— You should be on time tomorrow. There is no______ for being late again.
—OK, I will.
A:excuse
B: need
C:time
甲、乙两个电源的的路端电压U和干路电流I的关系图象如图所示,若它们分别向两个定值电阻R甲、R乙供电,可推知正确的结论是()
在“观察洋葱鳞片叶表皮装片和叶片临时切片”实验中,下列操作错误的是( )