下列化学方程式中,不能正确表达反应颜色变化的是( )
向 C u S O 4 溶液中加入足量Zn粉,溶液蓝色消失: Z n + C u S O 4 = C u + Z n S O 4
澄清的石灰水久置后出现白色固体: C a ( O H ) 2 + C O 2 = C a C O 3 ↓ + H 2 O
N a 2 O 2 在空气中放置后由淡黄色变为白色: 2 N a 2 O 2 = 2 N a 2 O + O 2 ↑
向 M g ( O H ) 2 悬浊液中滴加足量 F e C l 3 溶液出现红褐色沉淀: 3 M g ( O H ) 2 + 2 F e C l 3 = 2 F e ( O H ) 3 + 3 M g C l 2
It is often ______ that human beings are naturally equipped to speak.
I can’t leave. She told me that I ______ stay here until she comes back.
—— Do you mind my opening the window? It’s a bit hot in here. —— ______ , as a matter of fact
It’s high time you had your hair cut ; it’s getting _______ .
My friend showed me round the town, ______ was very kind of him.