C:NH3+HCl=NH4Cl
D:2FeCl2+Cl2=2FeCl3
A:NaOH+HCl=NaCl+H2O
B:H2CO3=H2O+CO2↑
(3x-1x)n的展开式中各项系数之和为64,则展开式的常数项为( )
Please translate the sentence _______ Chinese. I can't understand it.
请观察如图,回答问题: