A:
B:
C:
D:
At the ____ (begin) of the meeting, they sang a song together.
方法一:2NaClO3+H2O2+H2SO4═2ClO2↑+O2↑+Na2SO4+2H2O
方法二:2NaClO3+4HCl═2ClO2↑+Cl2↑+2NaCl+2H2O