在“测量小灯泡电阻”的实验中,电源电压为3V,小灯泡的额定电压为2.5V.
低等植物细胞中心体移向两极时,下列几种酶最活跃的是( )
--- Has he returned the book to our library?
--- No. He has _______ it for several months.
日本的核泄漏事故导致许多人患病.这一事例说明( )