某学生用2mL2mol/L的CuSO4溶液2mL0.5mol/L的NaOH溶液混合,然后加入0.5mL的乙醛溶液加热沸腾未见红色沉淀实验失败的主要原因( )
A:甲醛量太少
B:硫酸铜量少
C:加热时间短
D:NaOH量少
The old man lives in a wooden house _____ , but he doesn't feel_____ .
What are they? They are monkeys.
当a<0,b<0时,把 ab化为最简二次根式,得( )