A:NaHCO3=Na++H++ CO32−
B:Al2(SO4)3=2Al3++3 SO42−
C:H2SO4=H2++ SO42−
D:Ba(OH)2=Ba2++OH−
计算:cot45°+tan60°2sin60°-cos60°﹣cot30°
____A. Happy birthday!
____B. How old are you?
____C. How many plates?
____D. Here you are.
____E. Show me nine.
严格地说,地球的形状是一个( )